I don't do LoD on displacement shaders because I don't know how close the final surface will get to the camera (other displacement shaders could put the surface right next to the camera, for example, even if the shader we're interested in thinks it's far from the camera). Even if that were not the case, you'd still have long render times on closeup surfaces.
I'd like to make the Alpine Shader look at its input displacement, so that its features flow correctly along some arbitrary input terrain. It would be easy if I didn't have to worry about speed, but I will need to carefully cache and reuse input calculations approximating the surface to avoid turning the slow Alpine Shader into the Never Ending Render Shader. (Problem is, for the reason I gave above, I can't easily decide on an LoD-based resolution for the cache, so it needs to be based on the feature scales.) But I think you are talking about inputs for modulating the parameters of the Alpine Shader, which would also be useful. That's another future project.
Matt
