I assume the biggest hurdle for Blizzard when it comes to playerhousing is generating the art assets to use as an expansion feature. But if you think about it, it's possible they've been slowly building towards it over the years.
Orc - WoD Garrison, Ashran and Draenor, BFA new portal hub and the Arathi warfront.
Troll - (missing) but there are a few things like the Arathi witherbark huts
Tauren - Legion Highmountain
Undead - Darkshore Warfront
Goblin - Random goblin assets in BFA, Motherlode dungeon, Darkshore Warfront
Human - WoD Garrison, Ashran, BFA Stromgarde Warfront
Dwarf - (missing) but there are a few items. Hasn't really seen a massive update since Cataclysm.
Night Elf - Legion Suramar, Val'sharah, Tomb of Sargeras, Azsuna... BFA Nazjatar... elven is widely available
Gnome - Mechagon obviously!
Player housing doesn't even necessarily need to be tied to a racial capital. I think it could be cool to see Dalaran have a few housing plots available. For me even, I still have a little sentiment towards the Legion class halls. Just being a citizen in a big city is cool if you're visiting or trading, but if you're a DK being in a necropolis or a Hunter being in a remote lodge, that just feels way better as a place where you hang out.
Will we see player housing?