Well I can think of plenty of models to make or sets. One would be a Mountain Valley with mountains and rocks and some stuff for a lake such as a boat and stuff that would go with camping. And that would also allow you to make caves and such or plan your map if you want to say map a world. Another one would be a side scrolling set which I don't think I've seen. Alien landscape set, Alien city set, Planet set, Gun set, underground base set, city set, crystal set, superhero set, grave set, Sci-fI building interior set, Egyptian tomb set, Egyptian set, Space Dock set, Interior space ship set. I have lots more ideas but that would have to come at a later time or something I might try myself. You most likely won't have time to do all of this.
Cyberpunk Environment, Modular catwalk set, ship internal set, Modular SciFi Hallways, spacecraft Consoles set, sci fi greebles set, Cockpit set as well.
I am considering doing more natural hills and mountains. I already have stalactites and such that haven't been released. Also, the beach expansion showed me that these can overlap nicely so I will use that technique more.