1st I would like a return of the pre-Legion model with no expansion wide borrowed power systems.
2nd Further iteration on M+ affixes, some of current ones are straight up boring (Fort and Tyra) and others just don’t work for certain dungeons.
3rd Bigger zones that are made with flying in mind (Storm Peaks, Icecrown, Uldun, etc.). And If pathfinder would still be the template it should be earnable from launch.
4th Diverse reputations. Keep a 1 or 2 that would be timegated via WQs f you must but add more that are kill a mod=rep, collect stuff and turn in=rep (really bottom of the barrel examples just to make a point).
5th Less time gates.
6th Cross-faction grouping for PvE and maybe cross-faction guilds
7th New class. I personally would like a Necromancer or a Shadow Hunter, but anything would do honestly.
8th More Allied Races or proper races.
9th Tone back the story. Currently this cosmology stuff we are doing is uninteresting and feels way too alien, I would like to have adventures on Azeroth again, fighting smaller factions like the Scarlet Crusade.