Okay, I think I see what you're driving at. But, if, for example, you created a nice Perlin procedural terrain in WM and added an erosion node, etc, and then imported that into TG2, wouldn't it still have to calculate the erosion on the perlin terrain anyway, somewhere down the line? I don't know how powerful your PC's are, but doing the final build on a 2048x2048 tile in WM with extra quality settings on the erosion can take up to half an hour on my machine - and it ain't the slowest in the world. I don't see why the same thing wouldn't have to happen in TG2.
No matter what, the procedure has to be calculated on the heightfield to get the final terrain.