Let’s say I have a shot of a road, live footage stuff. I want to put a plane on top of that road. The plane has been textured to have the same appearance as the road. Problem is the plane of course has hard edges and doesn’t blend in with the road. I want to feather the edges of the mesh but how?
Perhaps you could apply a ramp texture to the plane to be used as an alpha value to blend the edges out. But real roads often have irregular edges not soft ones 
Sounds like an interesting method, I’ll tinker around with it, though with the alpha ramp would one side be faded/feathered while the other side is completely solid or is there a way to make all 4 edges the same feathered alpha amount?
If you add your own color ramps then you can add fades to both sides. Not sure how to achieve the other ends sorry.