In theory I think it's a good idea, kind of like an DC-RPG where the characters are pre-generated but I think the downside is adding the Request/Universe into it.
People usually do a Universe for their own ideas and their own takes on things, somewhat the same as with the request-verse. You are asking someone to do their vision of something, adding players to that is almost asking for a melt-down or god-moding.
Setting a game based on one of the Universes or Request-verses isn't a bad idea, there are some awesome ideas out there, but I don't think lumping them all into one is going to work out like you think.
*my two coppers*
Added after reading the link:
It actually looks like a cool idea. I'd like to see how it works before I give it a shot though, I've been wanting to RP again