My grand list of updates that would make this park personally the best it could reasonably be would go something like this.
1. Spaceship Earth Renovation ( Already promised and relatively needed given the age of the last update and just how much communication has changed post-Smart Phone.)
2. Wonders of Life Building Renovation (I'd be fine with literally anything as long as the space is open. Honestly, the Play Pavilion is a pretty decent idea for that side of the park to give kids who can't ride TT, GotG, or Mission: Space more to do outside of the Mission: Space playground and jumping in and out of the Model Vehicles in the TT showroom haha. They should reference Buzzy though.)
3. Test Track 3.0 (Confirmed! And necessary, 2.0 stinks badddddd. I hope they give the ride more life like 1.0 had.)
4. Tuning up the effects on the Nemo & Friend's Dark Ride. (I've got a thread in the making about this, but this ride is in poor shape. And that's a real shame!)
5. Remaking Soarin' Around the World to be more atmospheric and with a greater focus on the beauty of real skylines, as opposed to CGI Landmarks and Animals that don't give the same wonder of human flight as Over California did. As well as removing the jarring Transitions and restoring SOC's oddly smooth jumpcuts between scenes.
6. A full teardown and ground-up build inside the Imagination pavilion turning Journey into Imagination into a wonderful, E-Ticket trackless ride with all of the same tech and budget as Mickey & Minnie or Rise. Figment has become so ingrained into the parks through marketing, festival tie-in's, products and merch in stores both inside and even outside of Disney World that he deserves to be given something huge. Journey Into Imagination deserves to be the dual Thesis Attraction / Headliner E-Ticket alongside Spaceship Earth. This is my biggest wish and the most important of any of these.
6. Giving World Showcase one more major attraction. Big Hero 6 in Japan, Mulan in China, Turning Red in Canada, something to fill out the back of the park and tie it all just a little more together. Coco would be perfect if it didn't already have a very cute, enjoyable, and incredibly low capacity dark ride already. It would probably mean gutting not just Three Cabelleros but the indoor dining and shopping areas as well simply to make space for a queue line possible of holding that many people.
7. Sora, Donald, and Goofy Kingdom Hearts themed Meet and Greet in the Japan Pavilion on select days. (I lied, this is more important than any of these. Non-negotiable.)
Frankly, especially after the hub (almost) completion, Epcot looks and feels great. It has some notable holes, but a good number of these feel pretty simple. It doesn't, or at least shouldn't, take 5 years to fix the effects and speakers on Nemo, or to rerecord some new drone footage for a better Soarin'.
Spaceship Earth, Test Track, and especially Journey into Imagination are the plots that should be up next for renovation. If only just to finish the nuEpcot project Disney has started here. Test Track is already confirmed, Spaceship Earth has been pretty dead in the water since it's announcement, and Figment is a known issue and golden child for the marketing branch at least. I hope these get tackled very soon. This park is so, so close imo.