I merged the two twin idea threads here... I think they've hinted at this since they introduced the Bad Twin book (we have discussion on the topic in Book References forum as well)... though I'll be honest, I'm not a big fan of it either. I hope they are more original than the whole clone idea, which has been done to death in sci fi... just my personal opinion. I would rather they put them in as genuine connections to show karmic relationships.
But valid, I do like your variation on this idea, that it's not to be taken as literally.. the emotional twin idea.