The German message boardDer Hip Joint
have something similar. The admins select a few movie posters, and the fanartists have a select period of time to make their version of it. Made some pretty snazzy fanart.
So I think it's a good idea, I say go for it. Then again, I'm not a fanartist so me opinion have very little bearing on this matter.
I know Leela would make a great Monica.
Amy would fit as Rachel.
Fry as Joey (a little dumb, but a nice guy) or Chandler dating Monica/Leela).
Which will make Bender the opposite of Fry.
Kif as Ross?