@Oscarfan - Ooh, it sounds painful! From what I remember, when MMW was still in pre-production (I think when they were first writing up the script before any set casting) there were going to be more Disney Channel stars in it. I could've sworn I saw Vanessa Hudgens attached to the project at one point, and even Zac Efron (possibly even Ashley Tisdale, Corbin Bleu and Vincent Martella or the girl that plays Ally from Austin and Ally) but as I said, this was a while ago so had they been in mind for being cast, they were passed over. Although I knew from back then that Ross Lynch and Bridgette Mendler were going to be in it.
@Drtooth - You have a point, but I've always had a feeling and heard other Muppet fans speculate, that there were always going to be three new Muppet movies as a sort of remake of the original trilogy. And in a sense, I can see it. The first original Muppet movie was essentially to introduce people to the Muppets (or at least tell the story of how The Muppet Show came to be) and The Muppets (2011) is a reintroduction of the Muppets to a younger generation that were either not around during The Muppet Show's first run or too young to watch reruns on the Disney Channel or Nickelodeon in the early 90s. Then we have TGMC which takes place in England and centers around these jewel heists going on, leading to the jewel thieves eventually framing Miss Piggy and the gang having to ban together to prove her innocence. Now with MMW, it once again takes place in Europe and Kermit getting framed for a jewel heist because one of the jewel thieves looks exactly like him (but with a mole) so the Muppets have to ban together to prove Kermit's innocence.
So going by that logic, since TMTM is about the Muppets traveling to New York to get their musical on Broadway, we could assume the third movie to follow MMW could very well have them traveling to New York for some reason.