With The Fantastic Four: First Steps being set on a version of Earth in the 1960s as part of the multiverse, it kind of makes one wonder what they could've been like if they were set on Earth-199999 instead. After Stark sold Avengers Tower, and before it was confirmed to be the Watchtower, there were rumors that it could've been the Baxter Building. As such, a user by the account name of RE7LECT put this together on DeviantArt as a concept if that was the case.
If you ask me, this would've been pretty darn neat if so. But since it isn't, I know we'll definitely find ways to make do with how it's being put into motion. But just imagine how cool a transition it would've been if Avengers Tower was converted into the Baxter Building!