Even if that were the case, I've read from people here that literally every character more than a few dozen fanboys would recognize is in the mural. (I regret that I didn't take a little time to look for myself when I was there a few months ago.)
Assuming that's true, and assuming a spot in the mural is enough to lock down rights to a character, then the "who currently belongs to which team/family/etc." line of thought doesn't really mean much, since it would only potentially free up characters so obscure that it wouldn't be worth Disney's time to argue.
Even if not, as I mentioned above, all of the core franchises are taken.
X-Men is out due to the Storm Force Accelatron (Storm, Professor X, Cyclops, Wolverine, Phoenix, Gambit, Rogue, Beast, Iceman, Magneto, many more)
Spider-Man is out due to the flagship ride (Spidey, all of the villains, Black Cat, JJJ, etc.)
Fantastic Four is out due to Doctor Doom's Fear Fall (Torch, Invisible Women, Mr. Fantastic, Thing, Doom, Galactus, Silver Surfer, etc.)
Hulk is out due to the coaster (Hulk/Banner, Rhino, Abomination, She-Hulk, etc.)
Avengers are out due to the Captain America Diner (Captain America, Ironman, Wasp, Giant/Ant Man, Thor, Hawkeye, etc.)
Daredevil is out due to the Kingpin Arcade (Daredevil, Kingpin, Elektra)
The only other franchises even worth mentioning are Ghostrider (who does appear in the mural, but nowhere else) and Deadpool (not sure if he appears anywhere - but he might fall under either X-Men or Spider-Man as a villain).
So in other words, Disney gets nothing of note, mural or not.