If I'm not mistaken I already saw a screen space SSS approach before. I think it was in the latest GPU Pro book. Might be the same author of course.
Calculating the SSS in screen space instead of texture space does really make things easier when you have many people in your scene.
Indeed, specially with deferred pipeline. But i think problem with full deferred and ssss is a limit number of buffers, unless going for dx10,11. I would not go for prepass method in dx9, cause it will drop performance alot.