Legion class design and class halls is simply way ahead of a lot of expansions which is why many liked it. I don’t think you need ping or the resilient key system for m+. I don’t think you need warband shared reputations or warbound gear moreover when M+ exist it is very easy to gear up. Reputations are also much less of a issue, they started to become an issue again in DF when they became all very timegated and that they started to add a lot more stuff coming from them.
Emerald nightmare was a joke anyway so class balance didn’t matter as much, but considering what they did with classic we would get last patch class balance which fix still a lot of stuff.
I’m personally not interested in farming artifact power or dropping rng legendaries same as I don’t really want to experience titanforging again. But the content is still great.
The problem with Draenor is mostly the lack of content and also polish. For me it would need some work and addition to make it feel good. I’m not a fan personally of going on after mop but we will have to see.