Custom scenery is something that could be added to the table, I'd say.
It's one of my main worries about Planet Coaster, for as far as I've seen and read, the devs have been very vague about the possible ability to import models into the game. I'm definitely pleasantly surprised by the building tools and the ability to create saved structures, but much like for instance RCT3 and especially Cities:Skylines, being able to import 3d models allows for far more flexibility. Especially if it's combined with the planned UGC tools, perhaps akin to the system of Cities:Skylines, in which players can not only share custom assets, but also custom props using which they have been created.