That could cause some problems (unless the idea of humans trying to pass themselves off as Muppets is used). I doubt that Disney would pay for a lot of new puppets to be built just for a quick 10-second gag, only for the characters to never be used again. Disney could reuse several obscure characters who only us hardcore fans are likely to know about (Leroy the Donkey, Lugsy, Flower-Eating Monster, etc) and try to pass them off as new Muppets who get rejected, but then we would probably complain or point out this mistake. Disney could take some old puppets and add some features to them, or completely replace some body parts, but I wouldn't like that (I don't want the Lips puppet to have it's hair, eyes, and nose replaced, and I don't want the Pops puppet to be altered to look like a young person). The best way to do this would be to have these characters be whatnots, as that would probably be the cheapest thing to do to introduce a bunch of characters who only apear for a few seconds, and maybe some new whatnot patterns can be built for this scene, to throw off the hardcore fans. But then it would be weird for all of the characters who want to become Muppets to be humanoid, and whatnots are rarely used for animal characters.