My idea, is basically a sticky rail(s). This way, you would be able to make things like roller coasters go upside down or even straight down holes! This and many other things! This is basically what the rail itself would look like:
The Rails and Crafting Recipe:
The green is of course the slime on the rails that allow you to stick to it. Please tell me what you think and anything I should add to the post! Thanks!
Rollercoasters are fun, but you shouldn't go too crazy with them. It's minecarts, intended to use them for mining. Automatically transport items form your base to deep underground. But do you really see a use for going upside down, apart from making cool rollercoasters? Me not.
Explain comparators, beacons and portals, then. Cuz they don't have a lot to do with mining.
The game has different aspects, as it's a mashup of different genres. (Maybe too many, but that's another argument.) Sticky rails wouldn't only be used for rollercoasters, but there are probably 1,000 practical applications. For one, we'd finally have a reliable, fast vertical transport system (powered sticky rail going straight up) instead of having to build redstone-computer based piston elevators, or rising-boat water column elevator systems, neither of which makes any darn sense.
What about building up speed as the tracks go downwards, then being able to use this momentum to get upwards? so if you travel down 10 blocks, you'd be fast enough to travel up almost 10 blocks. That would be god for rollercoasters and such as you won't need that much booster tracks.