The plan was most likely muppets, hence the reason it wasn't announced at the presentation. They didn't want to suck the air out of what is a great ride announcement for the studios. If it was animation courtyard, we absolutely know the day of the announcement or the day after.
They've now received significant pushback and I think it threw them for a loop. I don't think they figured people actually care about the Muppets still. So in my opinion this delay in where monsters inc is going, screams of panic mode. It's either they're rethinking where it's going. Or getting their ducks in a row for huge PR spin job to mitigate the terrible press they're probably going to get.