I agree with the DE getting closer, possibly trying things out, and Damon not liking Kat's thing for Stefan. I don't think Kat has any real feelings for either brother, she just has a sense of ownsership - so it's a sort of, if I can't have you no one can kind of situation.
I don't think Stefan will fall for Kat - I think there may be manipulation involved, and him doubting everything he's ever known, but full out falling for her? not happening. He'll be confused, and with DE getting together, hurt - and here I'd like to see S/M and S/B friendships evolve. S/M can start an 'Elena's exes' club. XD
Kat, I think will not be happy that Elena's got both the SalBros crazy over her - and will obv. at some point try to kill her where the SalBros and Bonnie will save her.
I'd rather DK getting together - or whatev, than SK. This will be what it takes for Stefan to realise the manipulations and control Kat had taken over his life. We know she compelled him to feed from her, but what else did she compel him to do? Maybe now we'll find out.