I agree, I want a treehouse like that, but...
I decided to go on a different approach with three trees
and some beams to get a bottom. Now I have a solid
foundation for a house. It will not be big. There's a lot
of branches everywhere so I must avoid making a porcupine.
I haven't started yet but I have tested with three trees and
it works.

The reason I asked about Forest Outpost mod was something
someone said about wanting a treehouse in the forest.
To me it is perfectly OK making a stand-alone mod with new textures.
It will not be ghosted. Small footprint 4x4 with branches hanging out.
The house will be 3x3 tiles and if you opt for a 2-level house I can try.