Update:
Tested the material on a landscape with slight modifications to use landscape layers instead of vertex colors.
As long as Epic is not actively trying to get proper tessellation working on landscapes I may have to rely on POM.
There are holes in the surface and the texture coordinates are a total mess for the World Displacement input.
Anyways here the video of my test:
After that I continued with the main material to add wetness. And I tried a different base material to find out what complications might occur.
Right know I only had to adjust the Height Multiplier for the new heightmap and the Snow displacement height.
[Edit]
Another base material I tested:
