The terrain editor seems very user friendly but at the same time powerful. I love the terrain blending idea and also the "invisible wall and bridges" idea. It really opens up the possibilities. For unit editing and stuff you guys should have a look at the Warcraft 3 world editor, it does a FANTASTIC job at that part (they have a VERY bad terrain editor so dont pay attention to that). In wc3 world editor you can edit almost EVERY aspect of a unit.
Anyways once again your terrain editor seems truly epic and i cant wait to try it out