So I've been thinking, people were talking about a 'break' from world endangering tasks and wanted something. What if we get a different 'threat' apart from anything discussed. Kind of like Pandaria did for us. I can imagine we would visit Dragon Island as one way or another the black dragonflight is causing havoc under the leadership of Wrathion, who in some way still was corrupted or just plain evil in the end. This could also happen around Kul'Tiras, but I don't see that working here. The Black Dragonflight is trying to kill of 'lesser dragonflights' as they see themselves superior (Queue in the Chromie scenario). It is up to us to join and strengthen the other dragonflights to fight the black dragonflight (and maybe some close greater lore ally, I dunno, Naga, Ethereals, whatever would fit lorewise, since I'm not lore savvy). It could tie in that the Black Dragonflight had been (or was recently just before the start of the expansion) corrupted by the Void, granting them renewed strength. This would tie in the void as a continued theme for the next expansions.
I'm not saying I see this happening, I was just trying to think of different ideas. Kul'Tiras seems likely, I'm just trying to find different ideas