Apparently Nolan let on a short while ago that he felt the world of Inception was "a world where a lot of other stories could take place", and he plans to explore other possibilities through the medium of a video game.

"One thing we are looking at doing is developing a video game based on the world of the film, which has all kinds of ideas that you can't fit into a feature film. That's something we've been talking about and are looking at doing long-term, in a couple of years."

Christopher Nolan looking at Inception video game UPDATE, News from GamePro

Based on what's been said, there's some chance it will be MMORPG-like in structure. It may not be around for a while (Nolan's currently working on a script for yet another Batman movie), but it certainly is an exciting proposal. I get the impression that Nolan plans to work closely on this, developing his vision to a different level. Any thoughts on what sorts of things could go into a game like this?