Why, thank you for this thread. It had completely escaped my attention until you mentioned it elsewhere.
I too think EPCOT is nowhere near as outdated as critics claim it was / is. A mere visit to EPCOT Center's proud remnants would prove otherwise: the ride by monorail, walking towards the mighty SSE, riding SSE and LwtL, walking WS lagoon. Doing that while turning a blind eye to toon fish and princesses makes for an experience just as powerful and engrossing as ever.
The irony is that old EPCOT feels less dated than new Epcot.
Future World could indeed easily have been kept current. It was never as reliant on showcasing contemporary technology, never mind future tech, as much as it is sometimes thought it was. It was designed to be more timeless, and easily updatable to boot.
And even where it is outdated a bit, why should that matter? Main Street has long since stopped being about living nostalgia as it was to elder guests in 1955. Western and Exotic Adventure movies ceased to be movie genres half a century ago. Yet their lands function. EPCOT as an essentially 1980's World's Fair would be brilliant. Who would destruct that 80's World's Fair remnant of one century earlier again, the Eiffel Tower? Surely its technology has lost its wow factor now that skyscraping steel structures are erected in every provincial town?
For me, "outdated" means what you said about Future World: could have easily been kept current and showcasing possible futures.
The hydroponics that used to be so leading edge in the Land are now common, but there are even more remarkable technologies being used and experimented that could have highlighted there now.
The original core intent of Epcot is not outdated, just not being executed on very well.
But when you use Main Street et al as an example you're conflating two different originally stated purposes for being. Epcot was not stated to be about the past, eras gone by, it was positioned as forward thinking. The others were built for the opposite direction.
Maybe what you perceive as old Epcot being less dated than new Epcot might be because there is no soul, or mission, or higher whatever involved with the newer version. Its not a question of being outdated, its more like a lack of vision, there's no forward. The old Epcot, even if the tech or ideas have been superseded by reality, still PRESENTS a vision. And its fun to see what those in the past thought of the future - its one of the appeals of the CoP.
This really is a good fodder for a sit 'round the campfire all night talking sort of discussion.