Let me add my $.02 here (which will be an unpopular opinion).
First off...if Epcot was still the E.P.C.O.T. Center from 1982, it would be vacant aside from a few hangers-on.
Let's look at the lineup. Universe of Energy. A 45 minute slow-moving theater ride whose payoff was dinosaurs. Imagine that today? I'm not even talking about the even-worse Ellen's Energy Adventure. Since, in 1982, Wonders of Life wasn't around, we can skip that. Move on to Horizons (which, back then, was my 2nd favorite Epcot attraction). A slow-moving omnimover with a "choose-your-own-ending." This was unique...and may still be a draw today. Then you have World of Motion. A slow-moving omnimover showcasing that history of transportation leading up to the possibilities of tomorrow. Spaceship Earth...a slow-moving omnimover showcasing the history of communication leading up to the possibilities of tomorrow... The Land...a slow-moving boat ride with a few animatronics, sets, and then through a greenhouse. The Living Seas...an aquarium with a cool setting (SeaBase Alpha was a really cool "setting" but the ride was so short that it was pointless.) Imagination...my number 1 attraction at EPCOT Center. Sure, it was a slow-moving ride but the visuals, the feeling, the "imagination" put into it is something that will always be remembered...and pair that with the needle-tables, rainbow tunnel, etc. and you have a truly special and unique area. Smack dab in the middle of Future World was Communicore...cool...but would it work today?
Moving into World Showcase you have a slow-moving boat ride, the American Adventure, and a handful of movies as attractions. (Mind you, we still have all of those...plus another boat ride)
Now, let's be honest...even if you were to take those exact rides and update them with today's technology but leaving the feel and similar ride systems, do you really think people would be clamoring to visit Epcot? People need some "BAM" attractions to get them through the gates. When I first saw Spaceship Earth as a kid...I thought, "WHOA...I can't wait to go in there and ride it!" When I boarded and you start up the dark incline...I thought it was going to be awesome, only to get to the top and realize it's a slow-moving omnimover ride. Do I like it? Of course...but as a kid, I was disappointed.
Universe of Energy has an amazing building but is pretty boring. In today's world, people don't want to commit to a 45-minute attraction (especially if they will only visit once in their lifetime). I'm a big fan of attraction times being longer but 45 minutes is a little much IMO. Even a 45-minute Splash Mountain would turn me away. Do I think Guardians of the Galaxy is the answer? NOPE! They could've really put their heads together and developed an attraction based on Energy and Energy conservation just as easy as they can shove Guardians of the Galaxy in there (and I love the Guardians of the Galaxy!). GotG is a pure head-scratcher to me...but I'm holding out some hope that they do tie it in with Energy and the original feel of EPCOT. This is a case of just using the name as a draw to get people in...not necessarily the attraction itself.
Mission:Space is a failure. Updating Horizons with today's technology and maybe adding to the idea of "choosing your own ending" would've been a better option. The idea was sound, the final product wasn't.
You hear of an attraction called "World of Motion" and you get the feeling that it should be thrilling. Nope. This was the perfect place to revamp and add a thrill ride. I prefer Test Track over World of Motion. It's a thrill ride that's not too thrilling and most people can ride it without issue. (Sounds like an idea Walt would've liked).
The Living Seas should've been where a cool submarine ride went (not a thrill necessarily). Hopping on an omnimover and going through a tunnel is pretty "unimaginative." Adding Nemo to this one doesn't bother me. While I liked SeaBase Alpha, EPCOT was about edutainment and kids love the Nemo characters. The Nemo characters are there to get the kids interested and make learning about the sea-life fun. This might not be the best "update" but I don't mind it at all...and the ride is much better now IMO.
The Land, now, still has the Living with the Land attraction but added a non-IP "thrill" ride which focuses on the world we live in. Seems like a perfect pavilion in its current state. Food, thrill ride, movie attraction, family ride, and you can learn while having fun...it checks off every box.
Imagination is a mess. Personally, I feel this is the attraction they need to address the most...along with the ending to SSE...
World Showcase still has the boat ride in Mexico...although IP based (and if COCO comes in, it'll fit even better), Frozen Ever After as a single attraction is lightyears better than Maelstrom...but it's put in the wrong spot. It doesn't do anything for Norway aside from get people to visit the pavilion to go on the ride and meet the sisters. Norway has just turned into a Princess Mecca which is pretty sad.
Rat will be a great addition...it fits with the theme of the pavilion, it's truly an ADDITION and nothing that is currently there will be removed, and will hopefully pave the way for more additions to other countries. This is the way to add an IP without just shoehorning it in. (Much like a Brother Bear inspired Raft Ride down the mountains would fit into Canada, eh.)