What kind of IPs could add Uni in the future to UEU that could work and be popular and of course feasible for getting their rights.
Of course Middle Earth would be amazing and first choice.
Uni should bet also on Anime/Mangas. Some of them are superpopular in western countries for ages i.e. Dragon Ball, Saint Seiya, Sailor Moon or Doraemon.
What about Sports? Or music? Popular TV series or shows? Westeros? An 80's Nostalgialand?
A little late for Westeros.
Middle Earth might be more likely if it wasn't third party, but I can't count it out.
Anime/Manga, maybe a Dragon Ball land, but it feels like the time has past for that. Anime has significant niche appeal, but even the huge Dragon Ball Super movie that came out this year only made $30m Domestic, and that was considered fantastic. Anime, Manga, and Japan in general just doesn't dominate the culture like they did during the 80s. Maybe though.
Universal owns the rights to Wicked and they have the film rights for Dear Evan Hansen, so maybe a stage in the Hub where they play short productions of musicals. They have a theatrical group that develops musicals from time to time, so it could be a good little people-eater.
Depending on how Scoob does, a Hannah Barbara land could have potential. Have it connect to the UCM land to keep continuity with the Scooby Doo ride.
I have no idea how much of DC the Six Flags license covers, but if it's just individual characters, then they could squeeze in a Shazam ride or something. Less likely, considering the fact that Shazam didn't do great at the BO, but still.
EDIT: If they ever make Shrek 5, then that's something to consider.