"And how the heck is the director going to handle the incest vibes? Are the scriptwriters just going to downplay it somehow?"

At the risk of spoiling the later books, the incest bit isn't *quite* so problematic. In CoB at least, Clary doesn't do anything overly affectionate with Jace after the big reveal is made. She still loves him, but doesn't kiss him or anything (or if she did, I blocked it out -_-)