Me, you, or whoever: Don't look for anything like a "Seinfeld" movie for another 10-20 years, if ever. Jason Alexander and Julia Louis-Dreyfus are just young enough, talented enough, and proud enough to think they can create other characters, so when people see their pictures they won't see George and Elaine and only George and Elaine. I think that's a pipe dream, but dreams like that die hard.
The 60s-TV Batman & Robin, Adam West and Burt Ward, spent years trying to run away from their characters. They never did, and their show was only on for 2 seasons. They finally gave up (if you can't beat 'em, join 'em), and cashed-in on whatever cache their TV roles still had, which wasn't much by that time.
Personally, I'd like to see Elaine/Julia in prison, in a "Caged Heat" kind of movie, maybe with Elisha Cuthbert and Beyonce as cell mates. Maybe Elaine gets a conjugal visit from Brad Pitt or Ewan McGregor. Conjugal-visit sex with Elaine. Now THAT is happening.