I think it would be good if they added a 'Forbidden Forest' section to the Wizarding World, with a top scan ride themed around Aragog the spider.
Also, it would be nice if they re-themed either Toon Lagoon or the Lost Continent to 'Middle Earth'. Popeye and Bluto's Bilge Rat Barges could possibly become 'The Shire Barrel Boats'.
A Jurassic Park expansion also is needed. I like the idea of a 'Pterodactyl' flying coaster, a 'Lab Tours' dark ride near the Discovery Center (perhaps an omnimover?), and also a re-vamp of the animatronics on the River Adventure, they are starting to look slightly dated.
An expansion of Seuss Landing, to include a Mt. Crumpit Coaster (from The Grinch) similar to Big Thunder Mountain would also be great, as well as some kind of Lorax attraction.
And it would be great if they re-themed Marvel Superhero Island to 'DC Superhero Island', and perhaps added a few new rides. This is because obviously Disney have just bought Marvel and also if Man of Steel is a hit Superman and Batman attractions will probably attract bigger crowds.
Over at Universal Studios, I think an expansion of Springfield is already underway, so the only thing I would say is perhaps replacing Fear Factor with a Fast and Furious stunt show (although that might not go well next to the Wizarding World expansion), and in the future replacing Shrek with another 4D film, maybe Hop or another Illumination one?