Professortango is a reliable poster who I've never seen make things up or given me any reason not to trust that he was really told this by someone in the know. Of course things can change, but I think that this is very likely to be true. Makes sense too, if they are going to close down the center of TL after the 60th, they'll need to be able to leave a path to Space Mountain. This would let them finish a path through the current site of Innoventions to allow access to SM so they can then remodel the rest of the land.
You have to keep in mind too that this will be a really complex demolition project so it will take some time. The old Carousel theater is a complex building with lots of big heavy parts and the Autopia is even tougher with it blended in with PM tracks, Monorail tracks and the Subs building. Lots of stuff to avoid damaging and it will be very difficult to get big equipment in an out of many places. It just wouldn't surprise me at all to just have walls go up one day soon, this is a huge undertaking that is going to take some time. Probably doesn't make sense to announce what will go there for a while because it will be so long until it opens.