1. Ethereals and Arakkoa to be playable, pref. Arakkoa for the Alliance and Ethereals for the Horde. The now-neutral sect of Arakkoa in Outland follow the Naaru and thus are Light-worshippers, and they add a large amount of diversity to the Alliance. They also seem very intelligent and not inherently evil. Ethereals just seem like a fit for Horde, with their moral ambiguity and their exile from their homeworld. They're essentially world-travelling outcasts, something orcs and to a lesser extent pretty much all other Horde races can empathize with. It almost seems like too perfect of a fit if you think about it.
2. More engaging, challenging and fun content that is not raiding. After eight years of playing this game and mostly raiding since I hit 60, and then 70, then 80, then 85, then 90, I'm frankly burnt out on raiding and I know many other people who are as well. The system is no longer entertaining and I'd like to see more 5-man and solo content. MoP improved this a lot and was a step in the right direction, with Brawler's Guild, Proving Grounds (seriously, getting Endless 30 as a healer when I've pretty much never healed a raid was pretty brutal), Timeless Isle and world rare spawns stand out.
3. A continent where flying is restricted entirely. Controversial, maybe, but flying contributes nothing but further spoiling the lazy and impatient people.
4. Rethinking the changes they made to Affliction and Demonology warlocks. I hate to say they might need another revamp after they already got one so soon, but I don't think it has to be that far. Just put aff more on the focus of multidotting and revert Haunt to the way it was, and set Demonology's starting fury to higher or even just take it back a cooldown reduced by procs.
5. Old talent trees back in at least some form. Illusion of choice? Maybe, but making wonky hybrid specs, and just in general messing around with talents was fun and there's really no reason they were removed. It made alts feel more fun and just in general made the game feel more personal.