Well, Boyle recently noted that while he'd like to make another film, his schedule is jam-packed with projects; directing a stage play of Frankenstein in London and then acting as a creative chief on the opening ceremony of the 2012 Olympics. Screenwriter Alex Garland also recently said that the franchise itself had some rights issues that could be a hurdle.
Asked again about the the sequel that everyone wants to see at a recent press conference for "127 Hours," Boyle discussed the project at length, expressed major interest in directing a follow-up, but said currently "there is [only] an idea and no script." He did note that while an executive producer on "28 Weeks Later," he had very little to do with the Juan Carlos Fresnadillo-directed film.
"I'd love to direct another one of it, actually," he said. "Because I watched the second one and I wasn't that involved in the second one, and I really enjoyed watching it as a [spectator]. Because when you make films, you never really see them like a [average movie-goers sees them; it's weird. You're entrusted with editing a film for an audience, and preparing a film for an audience, yet you're as far away from what they will see as you will ever get, because you've watched it a hundred times and minuscule-y produced it. But I watched it as a [outsider] and thought 'Ah, I'd really like to direct another one.' That's where that came from. It's really a matter of time."
When asked if he would direct the film after 2012, he quipped, "If we're all spared." Boyle did give away one tidbit, revealing the picture "might be" set in Russia and he joked that Aaron Ralston (the real-life mountain climber character James Franco plays in "127 Hours") could possibly play a zombie in it. There you have it. File this project under so far away, yet so close. Boyle didn't address any of the rights issues Garland mentioned and the it's "only a matter of time" comment bodes well, but with a packed schedule and no one actively working on the screenplay, fans might be waiting even longer for another frightening zombie-pocalypse.