I think Wall-E shows how technology can co-exist with humanity, nature and be used to benefit everyone when used responsibility. The credits of it outright depict that and one of the main themes of Wall-E is that humanity must get themselves back on track without the unhealthy overreliance on technology.
"Now our Future World draws near ... and we face the challenge of tomorrow. We must return and take command of our Spaceship Earth ... to become captains of our own destiny ... to reach out and fulfill our dreams."
Wall-E fits in EPCOT, it's just hard to point to a pavilion for him to go to. If only there was a place in EPCOT that showcased technology where he'd be a great mascot for...
Wall-E fits better in EPCOT than Tomorrowland in my eyes. Tomorrowland is a future "that never was", WALL-E is both a cautionary tale and a story about co-existence with technology and how to do it healthily.
I find Wall-E and a plausible inclusion in EPCOT no different than Nemo being apart of The Seas, where it connects to one of the themes of the film and can be used to 'plus up' a space. Besides, we have Moana and Guardians of the Galaxy in EPCOT now, if anything, WALL-E would heal EPCOT more than damage. You really can't get worse than shoehorning a Moana attraction into EPCOT.