He elaborates on the Brody-Carrie dysfunctionality: "I don't think those two could be together -- can you imagine them being together and bringing up kids? They'd be in the divorce courts very quickly."
Admittedly, Lewis only knows what happens up through Episode Six of the new season, saying the writing of the show is "a much more spontaneous endeavor than you'd imagine." So this is just his point-of-view. We can hope the writers have their own!
Maybe there's late-in-the-game hope for Nicholas Brody and Carrie Mathison, after all.