The Experimental Prototype Community of Tomorrow had no chance of succeeding, for a number of reasons, the biggest issue being one that has plagued Disney for decades: chasing the future.
Ever since Disneyland opened in 1955 with Tomorrowland as one of its six major lands, this has been a problem. Initially, Tomorrowland was set in 1987, the year Halley's Comet was set to return. While that may seem laughable today, keep in mind that the 2030s and 2040s seem like far-off neverlands to us in 2019. But Walt and the Imagineers immediately ran into problems with the land, mainly revolving around the question of "How do we create the future... today?", because if you create the future, then isn't it the present?
During the 1950s and 1960s, Disney made an honest effort to create a Tomorrowland that felt like the future. Things like the PeopleMover, the Monorail, Adventure Thru Inner Space the Submarine Voyage, the House of the Future, and even the Matterhorn Bobsleds (part of the massive 1957 additions to Tomorrowland, and featuring the world's first roller coaster with tubular metal tracks, enabling smoother and more drastic turns) and Autopia (Los Angeles' freeways were new and exciting at the time) all capture that feeling. When the EPCOT Center first opened, it felt like Tomorrowland's perfected version in the Future World section of the park.
But keeping up with the future is not easy. Inside of Spaceship Earth, the final scene representing computer technology changes seemingly with every refurbishment, due to it advancing so quickly. Perhaps the best example of failing to keep up with the future is the Monsanto House of the Future, which was just inside Tomorrowland's entrance from 1957 to 1967. It was never updated, and by the time it closed, the main selling points of its futurism--plastics and a microwave, among other things--had become commonplace.
Picture that on a scale times a thousand, and you have Walt Disney's original idea for E.P.C.O.T. It was supposed to be a place where all the technology would be cutting-edge, from your wristwatch to your automobile. It was to be a playground for tech companies to test out their newest technologies by providing E.P.C.O.T. with prototypes. All of E.P.C.O.T. So every time a new type of refrigerator is made, a company would send thousands of prototypes to Florida, to be installed in every single home in the city. By the time that could happen, it's likely a new, better refrigerator would already be on the market by another, or even the same, company. It's the definition of throwing money down the drain.
While we're on the topic of money, E.P.C.O.T. was going to be exorbitantly expensive. Nevermind building an entire city in a Florida swamp--Walt wanted something like two layers of streets underneath the city, so that no vehicles would have to travel on the surface and risk hitting pedestrians. This was something he would not back down from. The only trouble is, Florida has a ridiculously high water table. It's the reason why WDW's Pirates of the Caribbean only had one waterfall drop, while Disneyland's has two: if they dug down any further, they'd hit water. So, with that in mind, to construct the tunnels under E.P.C.O.T., Disney would have to build them above the ground, and then build the entire city on top of that. They used this tactic to build the Magic Kingdom's Utilidors, a maze of hallways and rooms under the park to provide maintenance and other things without guests seeing that and ruining their immersion. This made MK infinitely more expensive to build, and by the time the actual EPCOT Center was built in 1980, the idea was scrapped and Disney built a complex of buildings in a circle surrounding the park, allowing cast members to enter from behind the buildings outside of the park. So, building E.P.C.O.T. with not one, but two Utilidors beneath it is one hell of a task, and something that would, in the end, provide very little bang for Disney's buck. And since this is 1970s Disney we're talking about--the same Disney that had been hovering around the "in the red" mark since Steamboat Willie, no bang for your buck is a death sentence.
The original Experimental Prototype Community of Tomorrow is a utopia. And utopias don't--no, can't--exist. As a lifelong admirer of Walt Disney, that is something painful for me to say, but it's the hard truth. If Disney had gone through with building E.P.C.O.T. with Walt still dying in 1966, the company would be bankrupt or bought out by the Bicentennial. If Walt had still been around... not much would have changed, sadly. This was one of the only times the legend bit off more than he could chew. The only thing E.P.C.O.T.'s construction would accomplish is creating a massive, city-sized blot of ink on Walt Disney's otherwise clean ledger of success, and leaving a vision of a utopia that would never be rotting in a swamp.
The Experimental Prototype Community of Tomorrow would be a failure if it was made. There's no getting around it. It would fall hard, and take down Disney, and Walt's legacy, with it.