StormDragonJr said:
Rollercoasters will go into space.
They will be miles long, and last for 30 minutes.
Invert more than one hundred times.
Go at speeds faster than some planes of today.
And will kill you.
The rides themselves can change till the cows come home, but our human bodies won't. We still have limited forces we can handle and can't exceed.
Think about it: The maximum velocity of most objects can be reached by about 2,000 feet. Building that even would never be cost effective. It's why we have very few 250+ rides now. And if a ride exceeds 1,000 mph, I'll eat my hat. The friction and forces involved would make it a mechanical nightmare.
I'm sure someone will correct me on some of these things, but you get the general idea.
On topic:
I agree with most of the people saying that psychological thrills would be cool. However, everyone is afraid of something, and it's different for everyone. Example being I'm terrified of just the simple observation tower (See Kings Island), where as others don't give it a second thought. I know some are afraid of the littlest bugs which to me seem laughable. Psychological terror and thrill are never a perfect ideal. As such, it might scare some, but never all like most coasters do.
As for the coasters themselves: the idea hasn't changed since it all started, just the way it's presented. There will be many different ways we'll come up with that will deepen our need for thrills. Keep in mind: the simple corkscrew coaster was terrifying when it first came out, and we all consider it very mild.
Holy crap that's a long post.