Let me just say this: I want Kirk, Jim, and Craig to work on the next film (if there is one) not just because they have experience with the Muppets, but also because James and Nick seem to have a prejudice against post-Jim Muppets. In the last film, the only post-Jim Muppet to have a big part was Bobo, in this one it was Pepe. So I don't want them to be the only ones who work on a Muppet movie if they're gonna keep putting those characters to the side.
Let's get a little perspective here:
Late 1990's-Mid 2005's - Rowlf, Scooter, Electric Mayhem, basically every character who wasn't in the core Kermit-Gonzo-Fozzie-Piggy wasn't really recasted fully. Characters like Pepe, Johnny, Bobo, Sal, etc. were there to basically fill the void left by the others. Same thing with Sesame Street after the 70's. They can't have Ernie, Bert or Grover on the street, so they make these new characters to base stories/sketches around.
There's no "prejudice against post-Jim Muppets." That's just silly. There's hundreds of Muppet characters, some are a lot more popular and well-known than others. Sure, it's awesome that the likes of Afghan Hound and Wayne and Wanda got little parts in the films, but that's all they should get; they're not important enough to the core Muppet group to warrant anything larger. Scooter and Rowlf haven't had any major role since their performers died and look at where we are now: they're appearing in commercials
instead of Kermit and Piggy.
Besides, how many "post-Jim Muppets" have/had any lasting power? Johnny can't really work without Sal, who's gone along with Dr. Van Nuter. So that leaves basically only Bill's characters, and that's only Pepe, Bobo and Carl.
So, Nick Stoller and James Bobin aren't ignoring the more recent characters because of some made-up bias. They're going with a more established, core group that everyone remembers and loves more. You can't have a Muppet movie and give every character a big role; that's just A. ridiculous and B. bad storytelling.