Hugo Martin Scorsese
Martin Scorsese's “Gershwin
What Was It? Scorsese’s biopic of the great American composer George Gershwin.
What Happened? It was the victim of studio politics and indecision. “Taxi Driver” screenwriter Paul Schrader wrote the original script in 1983 which was going to be a big, lavish and epic production (you can read/request his draft here)—bigger than “The Cotton Club” in scale and scope. Then John Guare (“Atlantic City,” the play"Six Degrees of Separation") wrote the draft that Scorsese actually wanted to make. The movie was owed to Warner Bros., but they were eventually interested in another Scorsese picture (they also were skeptical about the cost/return prospects on "Gershwin"). “Ultimately, when it was time to do ‘Gershwin,’ they turned to me and said, 'We'd rather have one on Dean Martin,' ” Scorsese said circa 2004. The problem was, while Tom Hanks was eyed for the lead of “Dino” (Martin’s birth name), and Nick Pileggi (the author and screenwriter of "Goodfellas" and "Casino") was going to write the script, that one wasn’t even started, while “Gershwin” was ready to roll. WB wouldn’t budge, Scorsese and Pileggi “killed [themselves] working on that script” that eventually wasn’t to Scorsese’s liking anyway (too unflattering on the Rat Pack subjects) and it had legal issues to boot. So both are basically DOA now, though "Dino" got further along with casting—somehow John Travolta was going to play Sinatra and Jim Carrey would have also played a Rat Packer.
Could It Ever Get Made? Martin Scorsese has half a dozen passion projects he wants to make, “Sinatra,” “Silence” (which seems like it’ll be next), “The Irishman” (which will reunite him with the “Goodfellas” team plus Al Pacino), so in short, no. He's barely going to get to all of these as it is.
Terrence Malick, Badlands

Terrence Malick's 

"The English Speaker
What Was It? Specifics are notoriously scarce (to the tune of a single screenplay draft popping up once on eBay in 2010 before being snaffled away and never reappearing), but this highly personal passion project was based on the pioneering study by “talking cure” proponent and Freud forerunner Josef Breuer of 1880s psychoanalysis patient Anna O, a hysteric given to melancholia, personality changes and a form of aphasia in which she could understand only German, but replied in English, French or Italian.
What Happened? There are a few Malick projects we could have slotted in here (for a more comprehensive rundown, look into Lost and Unproduced Malick Projects here), but this one, along with “Q,” which largely morphed into “The Tree of Life,” and a film based on the same “Sansho the Bailiff” fable that yielded the famous Mizoguchi film, formed the trinity of projects that Malick got really excited about during his self-imposed 20-year Parisian exile. The screenplay, according to producer Bobby Geisler, one of the very few people ever allowed to read it, was “as if [Malick] had ripped open his heart and bled his true feelings onto the page,” while author Peter Biskind described it as “‘The Exorcist’ as written by Dostoevsky.” But perhaps because he felt so passionately, the project got sucked into the whirl of controversy and recrimination that surrounded the tortuous process of getting “The Thin Red Line” to screens. Malick in fact held the finishing of his war elegy for ransom, demanding in perpetuity rights over “The English Speaker” to ensure no one but him could direct it. The producers held out, though, and in the dust cloud thrown up by the eventual breakdown of the relationship between Malick, Geisler, and “The Thin Red Line” producer Mike Medavoy, it’s hard to see exactly where the rights landed.
Could It Ever Get Made? Assuming the rights are in fact Malick’s, there’s still hope for this one, but with a major caveat: the similar-sounding “A Dangerous Method” by David Cronenberg may have burned potential backers on stories of 19th Century psychoanalysis for the foreseeable future, despite how different, more philosophical and more metaphysical Malick’s approach would no doubt have been. But really, we have to ask, if this is the burning passion project that it’s always been billed as, why has New Prolific Malick not lit a fire under it already? We have to assume it’s either a rights issue, or simply that the passion of 1992 has been dimmed in the interim. We, however, continue to carry a torch.

Alfred Hitchcock's Kaleidoscope
What Was It? Alfred Hitchcock’s unrealized story about a necrophiliac serial killer in New York City who lures women to their death.
What Happened?: Perhaps his most famous unproduced project, “Kaleidoscope,” also titled “Frenzy,” (he'd use the title later) came at a time of crisis; Hitchcock was reeling from the commercial and critical failure that was 1966’s political thriller “Torn Curtain.” He evidently approached many writers including Robert Bloch (the author of the book “Psycho”), Samuel Taylor, and Alec Coppel (the writers of “Vertigo”), but eventually settled on his friend, playwright/screenwriter Benn Levy (Hitchcock’s 1929 film, “Blackmail”). In many ways it was a kind of prequel to the events of “Shadow of a Doubt”—the life of the killer before he went out to hide from the police with his niece. In a 2012 interview with The Playlist, Steven Soderbergh summed up what eventually happened quite well: the filmmaker lost his nerve thanks to the studio folks who planted doubt in his head. “[Hitchcock] wanted to come to New York and shoot a black-and-white movie that had real violence in it. [Universal chief Lew] Wasserman talked him out of it. Just said basically, ‘Don't do that, you'll fuck up your brand.’ He had this really hardcore fucked-up movie that he wanted to come and do on the cheap and the people that were part of the cottage industry that he had created all talked him out of it. I just thought, 'God, how horribly sad that we didn't get to see that.' " Indeed. [Shot test-footage can be seen here, btw.] To boot, it didn’t help when he showed the script to friend François Truffaut who found its unrelenting sex and violence too disturbing for his taste.
Could It Ever Get Made? Unlikely, though a screenplay was completed. And don’t let its namesake fool you. While elements of “Kaleidoscope” were recycled for “Frenzy,” the latter 1972 film shot in England was an adaptation of Arthur La Bern's novel “Goodbye Piccadilly, Farewell Leicester Square,” which also featured a serial rapist-killer, but it’s a different story.

Andrei Tarkovsky

Andrei Tarkovsky’s “The Idiot
What Was It? Tarkovsky’s take on Dostoevsky’s classic story of a holy fool enmeshed in a tangle of love between two women, whose moral fortitude does him zero good in a world of corruption and immorality.
What Happened? Throughout the 1970s, Tarkovsky tried and failed to make a film version of “The Idiot.” However he praised Akira Kurosawa’s 1951 version of the movie, and the "holy fool" figure can be seen in several of the protagonists of his films (“Andrei Rublev,” “Solaris” and “Stalker,” 1975’s “The Mirror” have several allusions to Dostoevsky’s work) and the novel was evidently always on his mind. According to Tarkovsky's younger sister, Marina Tarkovskaya, adapting the novel was a lifelong dream and the state-funded and controlled Russian government (who had to approve all such movies) would never let him make it and kept stringing him along. "Andrei dreamed about filming [it], but they casually told him: 'You are too young and inexperienced. Let some time pass!," she told the Voice Of Russia in 2012. “In the end, they kept feeding him with promises for 10 years, and that cherished dream of his life was never realized. Let me stress that Andrei was never a dissident, but the leaders of the USSR still perceived him as a stranger, a person with internal freedom, that was what they could not forgive." An August 1983 letter from a Russian Deputy Chairman, confirms that Tarkovsky had signed a contract to write an ‘Idiot’ screenplay for Russian film studio Mosfilm, but in an 1984 Italian press conference, Tarkovsky declared he would never return to the home country. He then passed away three years later at the age of 54.
Could It Ever Get Made? No. It's unclear whether a screenplay was ever written, but in the proposal he wrote, Tarkovsky stressed the impossibility and perhaps futility of it all. Adapting ‘The Idiot’ in his estimation was “tantamount to clay passing through the heat of an oven where it can either attain form—both fire-resistant and waterproof—or melt up into something formless and petrified."

Arnold Schwarzenegger and Paul Verhoeven
Arnold Schwarzenegger and Paul Verhoeven

Paul Verhoeven’s “Crusade
What Was It? An Arnold Schwarzenegger-starring, immensely violent, historical blockbuster epic with a nice line in shit-stirring controversies, including the faking of a miracle, the revelation of the corruption and venality of the First Crusade and the papacy at the time, as well as pointed commentary on anti-Arab prejudice and anti-Semitism. Exhaustive plot detail can be found here, and a breathless script review is here.
What Happened? So close, and yet so far … “Crusade” almost got made in 1994, despite its massive budget and what seems now like a seriously dicey concept in light of the heebie-jeebies Hollywood gets over anything the Christian conservative lobby might object to. But why wouldn’t it have? At the time, Schwarzenegger was the most bankable star in the world, and was coming off “Terminator 2: Judgment Day,” which had itself broken the $100 million budget barrier, and yet turned out to be the most lucrative film in Carolco’s history. Verhoeven was similarly hot following ”RoboCop” “Total Recall,” and “Basic Instinct” and furthermore had a good working relationship with the star, as well as a proven record in delivering high-concept popcorn entertainment that also shaded in satire or social commentary. The script had been worked over, a top-notch cast attached including Robert Duvall, Jennifer Connolly, John (or possibly Nicholas) Turturro and superlative “that guy!” villain Christopher MacDonald, with shooting scheduled to begin in summer 1994. But that was just a little too late—despite Carolco’s recent successes, they had overstretched their production capabilities and Verhoeven was, he claimed “too honest. I was stupid” when it came to the budget process—an assessment co-writer Gary Goldman agreed with, saying “[Paul] doesn’t really lie about budgeting, which is a mistake because there’s no way to get these movies made without lying." In fact, pulling out was itself costly, as Schwarzenegger had a pay-or-play deal in place, and several million had already been spent on preproduction. Costlier still, the shingle regrouped and decided instead to put their eggs into a different big-budget basket. That film? “Cutthroat Island,” which bankrupted them.
Could It Ever Get Made? Online geek petitions to the contrary, realistically "Crusade" is the kind of '90s production that wouldn’t get made anymore: aside from its controversial aspects as regards Christian history (waay more heretical than "Noah"), the era of the action megastar is kind of passed. Verhoeven himself has more “serious” projects about religious history in the works (read: probably non-Hollywood) so it’s very likely this one will remain forever a hypothesis.

Harpo Dali

Salvador Dali’s “Giraffes on Horseback Salad
What Was It? A 1937 surrealist comedy screenplay, adapted from Dali’s original idea called “The Surrealist Woman,” which was to feature the Marx Brothers as it stars, alongside a distinctly Dali-esque cast of giraffes in gas masks and dwarves as Groucho et al., the central woman and her suitor journey through a “surrealist cabaret.” 
What Happened? With Dali also a part of Jodorowsky’s “Dune,” perhaps the great surrealist is the patron saint of this list. From the details online (which you can read here), the script he wrote, which was only rediscovered in 1996, sounds like it would have been potentially the most amazing thing ever, but also very possibly borderline unwatchable. Groucho thought something similar, anyway recounting later about the project that while Dali had been enthusiastic, saying ”Have I got a script for you!”… “He didn’t. It wouldn’t play.” However Harpo liked it and carried on a correspondence with Dali, who even embarked on a short film scenario solely featuring Harpo, seeing as they got along so well and “liked the same type of imagination.” Sadly that never came to pass either, and when asked in 1973 about the project, Dali became enraged, beating at nearby pigeons with his cane and declaring “nobody would dare to do Dali’s script!”
Could It Ever Get Made? Nope, nor should it. I mean, with Dali and all the Marx Brothers now gone, what on earth would be the point? Some ideas can exist outside of the mind created them, and be taken on by other people—this, from everything we’ve read about it, is emphatically not one of those ideas.