Yeah, 4 to 5 attractions could fit behind IASW, along with 2 in Frontier and 1 in Liberty... removing the Speedway would allow another area to be opened up (4 to 5 more attractions for Tomorrowland without replacing anything). Rerouting the Jungle Cruise path along with a service road and reworking the POTC would allow some expansion to Adventureland (1 or 2). You could even relocate the Magic Carpets to the expansion area.
But IASW should move to World Showcase... I don't want it to completely go away. But rebuild, then bulldoze the show building for a massive Fantasyland expansion (Neverland, Arendale, Tangled, relocated Princess Fairytale Hall, Pinocchio). Philharmagic moves to Town Square. Mary Poppins takes over Peter Pan and Philharmagic. Sleeping Beauty moves into the old Snow White show building. The Speedway gets removed for Tomorrowland redo (there's a ton of space behind the Speedway that could be developed)