Yea, I read Eckhart's comments about returning and I was like "ooh, don't TEASE!". I think they could do a lot with his character - in conjunction with another villian perhaps (these things always have to have two villians to really put the pressure on poor Batman). I think, as you said, a split personality could potentially be really cool, and Nolan is an expert with the study of duplicity (see The Prestige). But then again, maybe it is best if we all move and get something entirely new. Who knows. I just really want more in this franchise!