After reading this thread i would say my own stuff, too!
Some ideas from you are really cool and interesting, but we should consider this realistic.
The human body has a limit for G-Forces, it counts for both, Vertical and Lateral G's. So maybe some Coasters in the Future would and could be higher and faster but we going slowly to the end of this line. Otherways no "normal" human can rode these extreme Coasters without getting hurt. Or we need all Protection-Clothes to ride these Coaster-Types. A Good Example for this is "Formula Rossa" @ Ferrari World in Abu Dhabi. Safety glasses are required (and provided) to ride this Coaster.
I see the Future of Coasters in "Hybrids". Some of these currently build, for example "Hades 360"!
Hades 360 is a combination of wodden supports and steel rails. So with new trains its possible to make inversions on this Coaster-Type. Maybe in Future we will see more of these Coaster-Hybrids with other Combinations.
Another way were to build Inversion-Types that exists currently rare. For Example a "Cutback-Inversion".
This Type of Inversion was build only once, on "Drachen Fire" @ Busch Gardens Williamsburg.
But i think, that in Future we see more 3D-Effects, Lasershows and all this virtual stuff along the ride, maybe more Dark-Ride Parts.
Well, in the end i think we should lay back an let us surprise what the Coaster Manufacturers and Amusement Parks will show us
.
Soo long,
Greetz Cheleste