Jim Lewis is, to me, sort of the successor to Jerry Juhl in terms of Muppet writers when it comes to movies - he really seems to have a lot of Jerry's sensibilities in terms of not just the characters, their personalities, and their interplay, but also the right balance of humor, heart, and edge. Much like Joey Mazzarino for SST, where it seemed as though he was becoming the new Jon Stone.
As for Frank, he seems to retain the mentality that he'll only get involved if he's asked to, but nobody is asking him.