There's always going to be new dynamics and tricks for each environment you make a RPG or trial track with, as if you made one in any of the United environments besides stadium, like eyebo said.
RPG is certainly going to be different because Canyon isn't stadium. And I thought RPG builders would welcome this with new concepts and possibly story ideas as well.
Especially once blockmix is implemented the vast amount of platform blocks and slanted structures, as well as walls will give you possibilities to build huge domes and dungeons, whatever you want to call them, while mixing in some other pieces in these areas like pipes (which you can drive on, just not as easily as in stadium), parts of the GP roads not normally used for driving (the smaller side roads and the shades above them for jumps possibly), using tunnels and small passages with platforms like in stadium. You could easily make a tough platformer or maze-like construction.
It's not going to be like stadium, but it will still be the basic concept of a RPG, and you'll be able to influence others with new ideas. Just be creative.