I had posted something similar a week or two ago. I was thinking of framework that would allow people to submit work and have a team pull it all together. Not going to go into detail as I realize the idea is still too complex.
But I realized something as I was trying to develop the framework. Creating one big game together has too many issues. But what does have potential is everyone working together to provide a tool chain to develop games. This is what is generally going on with people offering free apps, utils, textures, world editors. The only problem is it isn't focused, and we don't have a checklist of what is needed.
I haven't finished working out my new proposal, but it would work something like this. Someone codes an input kb,controller,mouse handler. Someone else builds a 2D map editor. Some other people combine their work on terrain editors. Perhaps another group, shares it's AI scripting parser. etc... etc...
The goal would be to create enough tools that are flexible, work in conjunction with each other. Kind of like an FPSC creator. But it would have plug-ins to handle RTS's, 2D games, a little of 3D game maker, etc...
I still need to work on the idea, but if anything has potential, a complete tool-chain would be nice. In addition, a precompiler tool chain and processor that I think Milkman was working on. These are the things the community can work on together, in separate modules, in order to streamline game development for the community,