No meaningful suggestions really, but I was looking through my V4 stuff and the only conforming cape I could find was the Daz V4 Hooded Cloak... Not quite as long as the cape on your dress. It uses body handles, so maybe that would be a new challenge to attempt. Have to be honest though, something like that just screams dynamic. Probably why there seems to be so few conforming capes or cloaks.

Have you ever tried your hand at transmapped hair?