However, I too am concerned about the Garland quotes pointed out by Lee Bates, and their possible implications.
I wouldn't read too much into anything just yet. So far, I think the people behind the film are just being realistic: Dredd is an unknown quantity. It could easily enough become a lowish-budget hit, but it could also be a film that's highly regarded and gets a low box-office take. (Also, you never know what'll happen closer to release—it has 100% on Rotten Tomatoes now, but that could all change if critics start going nuts.) I love their enthusiasm for the material, but also respect Urban and Garland saying that if they just end up with one great film, that'll be good enough for them.
As for variables, that can mean anything, but it's not like Garland's the kind of person to swan off for a decade after writing a script. Just writing more scripts alone (and his point about returning next to a slower paced feature) could be what he meant. Regardless, I'm thoroughly looking forward to this film, more so as time goes on. And if this alone turns out to be this film generation's Dredd, so be it. At least the strip will have been properly on the big screen, rather than only having a terrible 1990s piece of garbage to its name.
