As others have said, I think it's quite possible, but very unlikely to succeed on a large scale, unless you have a hyper-talented community from which to pick and choose only the best people to work with (oh, and they have to be very motivated if you want them to actually stick around long enough to finish a game. Trust me on this). Letting just anybody in on the game will result in poor-quality output, such as what you see in many (but not all) PC game mods.