It's a completely sticky situation that you're facing, and i'm sure the decision you make will be one that's best for everyone. I have faith that you'll do what's best for the player base as a whole, since it should be the players interest in mind and at heart.
It makes a lot of sense either way. For instance, i didn't log in during the patch last night, so it's most likely i won't get a rollback. But for me to log in, and to see new players nearing the level cap would put me at such a disadvantage. So i understand it from that aspect. But for those who logged in last night, and grinded fairly, for them to get rolled back puts them at a disadvantage too. I know it's an unfair decisions to make, but it's one that may have to be taken. Either way, it's going to be unfair to someone. You just have to stand by the choice you make and hope people will follow.