I do think in theory, this sounds like a wonderful idea.
The main problem I see with it though, is amounts of people leaving.
Even I am guilty of this, if I map comes up that I don't like to play on I'll often leave, and I know a lot of other people do the same thing. With a random map thing, I can see a map that not too many people enjoy being the one randomly picked, follow by many members of the lobby leaving causes a game short of 24 players. Sure this isn't a big deal, that's just how I see this panning out.
I wouldn't mind to see this take place, it would be interesting to see what ensues.