Might be some rubbing issues but I doubt it, especially if you maintained proper tire ratio aspects in regards to sidewall heighth but with a smaller sidewall you'd probably be more prone to feel more of the bumps on the road (not as forgiving as a taller sidewall). I'm sure there are plenty of 19/19's and 19/20's rolling around right now.
You'd definately have to add 15" rotors to make it look just as pretty as the 18's with the 14" rotors j/k
