So, players will take an existing mountain top, and create a single switch-back path leading to the top, where they build an outpost?
Edit @Anni
Maybe the Heavy NPC's (and PC) can leave craters when they blow up? So you have to repair your battlefield.
Also, from the dev blog
it would likely induce completely flat islands, which is... undesirable.
This falls into the OMG Duh. Me, like other miners, have minor (or serious in some cases) OCD. I spent alot of hours in Second life making terrain flat (until they provided a single 'flatten land' button), and I even built a Land-Mower terraformer.
If it's possible to flatten an Island, I'll try it, and probably have alot of people willing to help (Long Live the Great Wall of Kent!).
If you don't want flat, or domes, or just generic looking islands if you will, then there should be something mechanically stopping me (and others) from doing it.
Also, under OMG, would be moats with castles. Anything I can do to strategically use TF, walls, and any other PBS to make assaulting it as difficult as possible, it will be done. Or if not by me, then someone