Personally i am really looking forward to finding out what the next expansion will be, but unless Blizz pull another MOP or WOD i think its pretty clear it will be Azshara and Old God related.
I would be quite fine with that, in fact i would be thrilled! Ever since WC3 naga have been my favourite race and i always lamented not being able to play them bar the few specific missions. Of course on top of the naga and Old God stuff such an expansion could and probably would include all that stuff which people are probably already sick of hearing, like Zandalar, pirate islands, other yet unseen islands mentioned here and there in the lore, ship garrisons etc.
BUT the one thing that could completely dampen my excitement for this theme is them expanding Kul'tiras to continent size, like they did with the Broken Isles. Honestly i think it would be an extremely cheap thing to make a single island the main (or Elune forbid even the only) landmass we get to see with such great potential hidden in and beneath the south seas...