The biggest issue for me is reputation. I wouldn't care about a class change if they would just make pre-expansion rep account wide. I actually do have a boosted char that I'm playing equal time with my main, but I CANNOT STAND that his rep tab is almost blank. He's still neutral with Undercity ffs.
Another minor complaint are things like fishing and archaeology. I can live without junk that isn't collectable anymore. But just the rep, that's all I'd need to give myself over to another main.