Hello, I'm new to this forum and new to being a Universal fan (50 year Disney fan from the West Coast). I see this conversation is not active but I have read all that's posted and wanted to add some thoughts, hoping you find worthwhile:
As far as the large 20 acre expansion pad... there are some genres the park is "missing" which include sci-fi as mentioned, a lush tropical jungle environment, and a historical/geographical adventure theme such as pirates or old west. None of these are required but could offer variety.
I would love a fully immersive 20 acre pirate themed land, though can't think of an IP besides the video game Sea of Thieves. I'd love a 20 acre old west (especially with that somewhat going away from Magic Kingdom) and maybe the video game Red Dead Redemption could offer the IP.
But the tropical jungle is most exciting to me in terms of what Epic is missing (other than taste at DKC) and one radical option is to build Jurassic Kingdom here. With the acreage available, they could build a fully immersive world with multiple ride vehicles...a new and improved boat ride, jungle jeeps (perhaps trackless like Magic Kingdom's upcoming Cars ride), and even a skyway/cable vehicle through the treetops. All of these ride systems could traverse the same expansive dinosaur-filled jungle similar to the Autopia/Motor Boat Lagoon area of Disneyland, offering different flavors of experience, and individual dark-ride scenes. This franchise is so core to Universal and could be reimagined on an epic scale. And I think it could have its own in-park Jurassic Kingdom Hotel as a backdrop, with lush plants and waterfalls from the hotel facade.
This could be especially smart given that Disney is removing dinosaurs from Animal Kingdom, and dinosaurs appeal to all ages, you don't have to be a fan of the IP to "get dinosaurs."
So what would happen to Jurassic area at IoA? There could be a Harry Potter expansion with The Burrow, Quidditch World Cup, and Velocicoaster could be re-themed as The Dark Mark, flying over the magical tent-city of the World Cup. Keep in mind this would be in 10-15 years after Jurassic Kingdom opens up.