Hello Lads, 

I've had an idea for a while to create a new kind of game, combining Tony Hawk's Pro Skater and Platform Fighters (Really, SSBM and/or Rivals of Aether). It'd have some combination of stage control mechanics a la Graffiti in THPS, Sumo-style Ring-outs a la Smash, those sorts of ideas.

What I'm trying to find out is,

Would this engine be conducive to creating platforms and terrain with specific properties? For example: Rails, Quarter Pipes, skatable objects in general, etc. I'd love some feedback on the idea.

Thanks!

It's definitely possible if you know how to make those mechanics in GMS2 already.
The built-in collisions probably aren't the best for that kind of gameplay (they're not very physics-based).
You can try out ideas in the free 0.7.1 version first to see if things work out the way you want.