If I had to pick an area of each of the two theme parks that I’d like to see redeveloped, I’d personally go with KidZone in Universal Studios Florida and the Lost Continent in Islands of Adventure.
KidZone does feel a little out of step with Universal Studios Florida’s other areas these days, however I’m not sure if it ever will be redeveloped as Steven Spielberg has reportedly threatened to sever all ties with Universal if they remove Orlando’s ET Adventure. If they ever replaced ET, I think a Mack spinning coaster like Space Fantasy in Universal Studios Japan (which actually replaced their version of ET) would be a cool fit, personally.
As for Lost Continent, it’s always felt a bit redundant as an area to me. I know it played a far more prominent role when IOA first opened, as one of the park’s flagship attractions (Dueling Dragons) was part of it, as well as Flying Unicorn, but ever since Harry Potter opened, it’s lacked a real star attraction (I know Poseidon’s Fury exists, but that does fade into obscurity a bit amongst the other major rides in IOA). All of the park’s other islands has a real star ride, if you think about it, with some even having two (Hulk & Spider-Man in Marvel, Dudley Do-Right and Popeye in Toon Lagoon, River Adventure and soon to be Velocicoaster in Jurassic Park, Forbidden Journey and Hagrid’s in Harry Potter. Scratch what I said above, all of the ones I mentioned have two!). To a degree, I suppose Seuss Landing also lacks a star attraction, but I feel like that area has a lot more to do than the Lost Continent on the whole. I do think a family roller coaster would be a nice addition to Seuss Landing (I do remember reading that an Intamin drop track coaster themed to the Grinch was planned, but with Hagrid’s now operating in the same park, I find it unlikely that that will ever get built), but I think it’s a pretty great kids area on the whole; very vibrant and colourful with quite a bit to do! With the Lost Continent, though, I feel as though it lacks things to do in comparison to some of IOA’s other islands. However, I must say that the theming in the area is incredible!
These are just minor nitpicks, however, and I’m probably being overly harsh; I absolutely adore both of Universal’s Florida theme parks, with IOA in particular being my current favourite theme park!