I was wondering...
Maybe the arches that are still empty in that shot in the official trailer are going to be filled by other secondary characters that might have prominent cameos in the film and they either haven't been put in yet or were edited out to not give too much away.
One thing that I think would be neat is if they do this:
In the Steve Martin episode of TMS, as we all know, some of the show's minor characters tried to audition for the show, but got rejected by the "major" characters out of fear of losing their jobs and getting replaced (Baskerville as a comedian, Lenny the Lizard as an emcee, Mary Louise as a female singer, etc.). Perhaps if they come to the theater to perform in the telethon with their fellow Muppets, perhaps they'll ask if they can do their respective routines (referencing their failed auditions in the Steve Martin) and get turned down, causing them to remain in the background, but when the "major" characters end up in jail (leading to that scene in the "Fuzzy Pack" trailer) while the telethon is in progress, they'll call the characters that are still holding down the fort at the theater to cover for them until they get back, including begrudgingly asking Baskerville to fill in as the comedian, Lenny to fill in as the emcee, etc., finally giving them a chance to shine in those roles, if only for a short while. And maybe those minor characters will fill the empty spots in the arches as well in the finished film.
I know that's a long-shot, but I wouldn't put it past them completely, due to Segel, Stoller, et al. being the big Muppet fans that they are and the fact that lots of little nuggets for the fans will be popping up throughout the flick.