Wow Oliver this looks impressive! Even though I am not doing anything with 3DGS while in school I will buy it soon just to play with it.
From looking at the video I wonder if it might be good to have a margin/border option for the height map generator? For example if you are creating an island and you don't want to manually bend all the edges of the hmp down you could set generate a border all around of a uniform height so that the outer edge of the hmp is all the same height -eveything slopes down or up to it. Hope that is clear.
