We know that Ahn'Qiraj was a lost titan city and that the Tol'vir were assigned to it, that entities like Ossirian were once watchers like Setesh. (Setesh's model is nearly identical to the Anubisath that patrol AQ today.) It just feels like, with C'thun obviously driving Cho'gall around even after his "death," that there's room for a whole raid just dealing with the lost connections between AQ and Uldum. The lost passages of the titan research facility that the Qiraji took over? (We know from Uldaman and Ulduar that titan constructions tend to go on for miles and miles.)
And that's hardly even the top of the list of raid instances we could see. A lot of us hoped for and expected an Abyssal Maw raid of some kind. There's a lot of talk about another Caverns of Time instance or raid with Nozdorumu's return. And I can't be the only one who keeps thinking that Grim Batol has entire layers we haven't seen yet. Heck, there are whole terraces in Deepholm we visit once and never go back to, and that whole zone is massive and cries out for more.