Not Terragen but some very inspiring work here.
I'm sure some of the techniques could be carried over.
The last three were done in Houdini
https://www.artstation.com/aronk
I know his work. Aaron is a very skilled landscape artist.
Great work. If vue was more stable and handled memory better I might use it but it drives me nuts.
Aron has been testing for SideFX's Houdini. Apparently they added some new terrain and landscape functionality. Images look impressive. All hos work is topshelf that's for sure
It's the Houdini stuff that intrigues me.
I think I may just have to get my learning hat on :)
ANd yes his work is very good indeed.
3D World Issue #231 (March 2018) has a feature article on Houdini including a section on "Terrain Tricks".