Also, I'm a bit late to this but I tried to give my (pessimistic) predictions on 10.0.
Theme
What I Want: An expansion that takes place on Azeroth.
What I'll Get: Dragon Isles expansion that starts out great but inevitably leads into more cosmic lore. I imagine we'll probably be visiting Zereth Vitae in 10.3.
New Races
What I Want: No new races. It doesn't work as a big expansion feature anymore, not ever since they introduced Allied Races.
What I'll Get: Some kind of dragon race to please the scalies. I imagine it would be similar to Au Ra from FFXIV.
New Class
What I Want: Dragonsworn: Available to every race. Has class-specific draconic customization like scaly skin, horns, cracked skin, and flaming eyes. Wears Mail and uses Polearms.
What I'll Get: Some kind of shitty Ranged DPS/Healer class that's as boring to play as it sounds.
Main Characters
What I Want: Murozond/Nozdormu, Alexstrasza, Wrathion
What I'll Get: Tyrande, Kalecgos, Jaina
New Features
What I Want: Something innovative and fun that doesn't feel like a job.
What I'll Get: Another terrible time-waste system designed to keep players logged in and subscribed for as long as possible.