Since integrating the grass shader, I've been thinking that a geometry shader extruding a couple of shells ought to be good for a lot of things - finally I've found the time to tinker with this.
Small-sized volumetric vegetation layer extruded between the trees - seeing this for the first time, I immediately realized what we've been missing forever - it looks much more real than just trees and bare terrain underneath.
But it can do much more - extruding some micro-structured rocky surface from the ground:
Might be a while till this is good to go, I still need to take care of pesky issues like lighting and fogging, but expect it for for the 2017.4 release.
Credit for coming up with the underlying technique goes to IcecodeGL of course!