Ok you keep missing the point entirely. The rides of then, if they had been properly updated it would have been amazing. You are assuming that somehow the only thing young people want is thrill rides and that is not accurate. Many of the hardest EPCOT Center fans were children when it opened. The kids were never bored because everything was inspiring and amazing. They could do that again but no lets just build big rides cause that's all the young ones care about.
I disagree. No matter how inspiring and amazing those attractions would have been, the image of Future World as a glorified science fair would have turned off many potential guests. The mix is the thing. If Magic Kingdom suddenly became Princess Kingdom, it wouldn't lure in many people with Y chromosomes. Sure, Dads with their little princesses, a few teenage boys with too many hormones, a few pervs, and a few of the more effeminate would bop in. But the vast majority of boys and men would stay away.
Similarly, Future World had to attract people who weren't turned on by science and tech. Again, "Fine, Dad, I'll go to Epcot, but only if we fastpass Test Track" is the sort of thing that many parents and group leaders hear. It's naïve to think otherwise.
Also, it was never seriously considered to turn SE into a roller coaster. From what I heard, the stresses would have been too much. Anchoring would have been a huge problem. Nevertheless, the fact that Epcot's iconic postcard attraction was considered for thrill ride transformation is an apt example of how desperately Disney was pushing for thrill rides. Rightly or wrongly, that was the perceived need.
Today, Epcot is the 3rd highest attended theme park in the US, in large part because of its mix. It's right behind two other greatly mixed parks: MK and Disneyland. Coincidence? I think not.