I think that would be great, in theory. There's the saying that too many cooks ruin a broth and I think that would apply to this situation very well. You're going to have a LOT of programmers if (hypothetically) everyone helped out.
Even if you used something like subversion to control all of the code and things you're still going to have a lot of people writing lots of bits of code of different quality levels. In short, i would probably end up being a mess.
So, with that in mind, you'd probably want to cut down the amount of programmers, so you'll probably end up with something like the average indy development team.
I know professional games development companies have quite a lot of developers, but with them there's the great motivator, money. If people start to slack quality wise then they run the chance of losing their job.
So yeah, that's my 2 cents. I'm sure you could organise this so everyone could help out. You'd need moderators and stuff like that. Other than the large glaring problem I've just pointed out, I think this could be a really fun idea and I'd love to help out. It would have to be in a .NET language though if you want me involved, I am NOT learning vb6 when I've already learned vb.NET.