Well, I don't know what you mean by "big kid". Do you mean that literally...like for teenagers (big kids) or do you mean for adults who are "kid at heart"?
Personally, I think there is a difference between the two...and I also think that Disney should build at least one E-ticket ride that would appeal to each group. My suggestions are:
A. Maleficent Coaster: in Fantasyland, on land reclaimed from demolishing the Speedway. Make this one for teens...and theme it as Prince Phillip racing through the thorn forest and ruins and battling the Maleficent dragon. Include lots of fire special effects in greens and yellows like in the movie, with that haunting score. The queue would be themed as a forest of thorns and the show building would have Maleficent's castle at the top.
B. Time Travel Coaster: in Tomorrowland, on the other half of land reclaimed from the demolished Speedway. Have this one be for older teens/adults (kids at heart) and have it be more intense than Space Mountain...with the theme being that it's a rocket that travels through time and you skip through different eras before rocketing to another one. Early life on Earth. Dinosaur age. Asteroid impact. Ice Age. Wild West. Distant Future. What's fun about this is that you could do a little homage to all the lands of WDW in just one ride (especially if you had a medieval pit stop in there). Theme the queue area like it's a research center where all the relics being collected from this time traveling are being examined so that guests will get more insight into the time periods they'll be traveling through before they ride the ride (so have display cases showing artifacts...and also have animatronics or video renderings of the animals that were found in those time periods).
C. Tron Coaster: Also for Tomorrowland, if the time machine idea is not good enough. This would be for older teens/adults and would be like you were zapped into the Tron game.
D. Adventurer's Club E-Ticket: Not a coaster, but something that would make you feel like you were on an adventure with the Adventurer's Club in Adventureland. This could be for teens. The show building would actually be built so that an Adventurer's Club Restaurant would be on the second floor or adjacent so the theme of the ride would be strengthened with the adventurers in the new club. The ride could be a mission that the club sends new recruits on...to investigate something or to capture some animal like a sabertooth cat or something from the jungle. Take the Jungle Cruise but remove the water and have it go at high speeds racing through jungles on the hunt for something, and have mythical animals be leaping out and scaring you the whole time.
E. Rapunzel Runaway Mine Car: There's a scene in Tangled where they have just left the Snuggly Duckling and end up in a cave...and then they get pushed out by water and end up in an area with mine cars and tracks...that can be expanded into a Rapunzel ride. Not sure where they would put it though because the Tangled bathroom area has no room for a ride like this. But to me it seems like a nice bridge between Fantasyland and Frontierland. When I watched Tangled I thought about that...because it was like the Rapunzel and Flynn characters left Fantasyland (the Snuggly Duckling) and then crawled through Frontierland-like tunnels and ended up in a desert looking area like the old West/Thunder Mountain. Too bad the entrance to a ride like this can't be built in Fantasyland next to a real Snuggly Duckling and then the show building would spit you out in Frontierland near Thunder Mountain somehow, using all that wooded land that's along the Rivers of America. I personally think it would be very cool to be deposited in a whole other land when we left the ride...but I wonder if that would be too disorienting for people who would be waiting for their friends to get off the ride and they'd be surprised that the ride deposited them on another side of the park.
I love thinking up new ideas for rides. I wish I had the know-how to be an Imagineer. My husband loves building model trains and I've tried here and there to get him to make one that's based on an idea of mine for a ride but he's never interested in doing this. He has his hobby (the trains) and I have mine (armchair imagineering!).
