When is an attraction announcement not really an announcement? When it’s published accidentally, that’s when. It’s no secret that the Prince Caspian exhibit has been moved out of its Sound Stage in Disney’s Hollywood Studios. There has even been some speculation about what would be going into that space on various fan sites.
Usually those exhibits are ‘sponsored’ by some marketing budget or another from the Walt Disney Studios. Typically the goal is to sell DVDs or build audience affiliation for a sequel. So it was assumed that the next exhibit would be for a movie that had seen some success (which means it has a decent marketing budget) and is likely to have a sequel.
If the first movie that comes to your mind in The Muppets, then let’s say Great Minds Think Alike. Other likely candidates include John Carter or TRON: Legacy. However neither of those have had sequels greenlit. So Muppets it is. It even already has a tie-in with DHS.