I agree with what @
Figments Friend said about substance and being educational, interesting, and inspiring. With today's knowledge, global community, and technology, we should be able to revitalize Epcot AND still provide the thrills and theme park substance that many others yearn for.
I've always been a huge fan of the concept of The Land pavilion. It is a destination much like that of the countries or a world's fair pavilion that discusses a topic and has different avenues to immerse the guest into it through rides, shows, food, & merchandise. Wonders Life was in the same concept with The Living Seas & Imagination close behind, but some pavilions just lack that substance. Universe of Energy (Ellen's Energy Adventure) at least still tries to provide that epic yet educational approach to a topic. Mission: Space & Test Track have really lost their substance and are more or less just attractions themed to a topic. Giving each pavilion more to do in one place is also great for educational purposes, more experiences, more merchandise/food opportunities, and also great for Florida's rainy seasons.
If I could revitalize (not redo) Epcot, it wouldn't necessarily backtrack to what Epcot used to be, but evolve into what it should be today using the same principles of yesteryear.
As you enter, Leave-a-Legacy will be gone, but perhaps with the right technology and incorporation with a natural environment, something similar could be erected along the plaza's sides that serves less like maze of tombstones with poorly etched images. Spaceship Earth is great still, not perfect, but really could use something to help bring the timeline from ending in 1980s to ending in the future. I feel like there was a backtrack over the years from mentioning the internet and it's global neighborhood to just ending at personal computers in garages.
Universe of Energy could really benefit from a complete overhaul. The building is huge enough to house a ride or two and perhaps an information film or kids play area exhibit at least. There is so much more that we know and or could discuss/present with energy these days. Not only in what I call "classic" energy sources, but definitely all the new renewable energy sources.
Wonders of Life, er I mean... the Festival Center has been serving good purpose as a Festival Center, but I feel like the old Odyssey Restaurant might also be just as useful. There is so much opportunity (and risk) with bringing back a pavilion on health and the human body. Even with a topic that is very personal and delicate as health, exercise, & the body, there are still way to present information. While I think that some aspect should be dedicated in nutrition, exercise, and taking care of your body, there are more adventures that can be had with the topic. Body Wars (although not ideal) really did present the body & modern medicine in a more thrilling & futuristic way. Also although The Land pavilion was home to Food Rocks and growing food, Wonders of Life has a great opportunity to introduce many guests to delicious but extremely healthy meals and brands.
Although I miss Horizons the most of any extinct attraction, the idea of a Space pavilion is still a great idea. Let's face it, Disney has tried to lure guests away from visiting other area attractions for years. Disney's Hollywood Studios covered the movies and Universal. The Living Seas & Disney's Animal Kingdom covered Sea World & Busch Gardens. Typhoon Lagoon & Blizzard Beach covered Wet n Wild. Mission: Space / Space Pavilion were a perfect way to cover the Kennedy Space Center. Mission: Space kind of failed to really prove itself as a space pavilion though. It didn't have as much substance as the other pavilions and was focused on more thrill. It also was rocked by some unfortunate incidents. Space exploration shouldn't be kept to sci-fi Tomorrowland or to thrill junkies. Space is full of beauty, mystery, adventure, and opportunity. How cool would it be to have a space pavilion that had rotational exhibits & attraction exeriences based on different planets for different times of the year? There is so much on space travel, but what about space living or life on another planet?
Test Track 1998 was an innovative way to bring the transportation topic into a more thrilling manner. It still was educational to an extent while fulfilling the need for more exciting rides. While I love and praise the current Test Track for its refreshing looks and futuristic aesthetics, it has lost some of it's substance. I'd love to see more of that substance return to provide more history and more exciting possibilities that don't just focus on cars, but also on planes, boats, and trains. As much as I agree that Epcot doesn't need more Pixar characters, adding Cars characters in a subtle way, would be a great way to get kids interested in the future of transportation.
Imagination is very lost right now. While Wonders of Life can focus more on the body and health and The Land can focus on scenic beauty, natural resources, and food, Imagination is purely about the mind and the 5 senses. With all the new ride technology out there these days, there is so many ideas that can come together to create a truly inspriring imaginative ride. There are also many great characters including Figment that can tell the story of imagination and what you can achieve with your mind. Imagination can also be a new home for a crazy snack bar that features imaginative selections that are outside of the box. Foods that taste like something completely different or foods that look like something completely different. This is more than purple ketchup and apples that taste like grapes, this would be a fun way to really excite the imagination and even dare I say please the profit gods.
The Land is the most perfect pavilion if there was one, but still has room to improve. Circle of Life needs to go and something with a similar message about recycling and being evironmentally friendly would still be welcome. Soarin' just needs to be updated despite it's already immense popularity. Living with the Land is perfect. Sunshine Seasons is perfect.
The Seas with Nemo & Friends has lost something in it's transition from The Living Seas. I love that Nemo & his friends are brought in to help educate young guests about the Seas and all the animal life in them, but the ride has lost it's futuristic wonder. Hydrolators are dearly missed. With many aquariums around the world being newer and more impressive, it's time that Disney takes theirs to the next level.
World Showcase is also pretty perfect in a lot of ways, but is starting to get greedy on profit and stray from substance. While I don't think every pavilion needs a ride or a character, I do think that a few should be added to help tell the story of many of these countries. Mexico could have a better ride. Norway could have a more updated ride. China has a wonderful film. A new country should replace the outpost that features a new ride, show, merchandise, AND restaurant. I feel Germany needs more cultural performances in a more public (less restaurant) setting. Italy would have a great chance to have a ride based on Roman mythology. The American Adventure is a perfect show, but more uniquely American food offerings would be great. Japan would also be a great location for a ride. Morocco could be home to a new show perhaps. France needs an updated film. The United Kingdom would be perfect for a dark ride about British literature. Canada has a great film, but still lacks substance in the rest of the pavilion.
So that's my lengthy opinion on the future of Epcot.