Is this clamping method applicable to any type of geometry, that nears the sub-sample boundary size?
"Yeah but does it support WAA!?!??"
Here's one method to sort per fragment.It seems like this can be generalized via contour detection similar to the cell shading methods, then expanding the edges and converting coverage to alpha.
Proper sorting will still remain a problem, but perhaps with DX11 there might be efficient ways to sort per fragment.
A quick idea : During development apply this to everything in your scene, and then only show (or highlight) the pixels that were affected, to detect good candidates to apply this technique to in the final product - rather than guessing what geometry it might be good for.
I did some tests on my own and you can indeed skip the texture lookup whenever In.Fade.x goes below 1, without being able to tell the difference.