I'm not expecting a "South Seas" expansion anymore, I'm just observing that despite Battle for Azeroth doing Zandalar, Kul Tiras, and Nazjatar, there are still plenty of canonical islands that we've never been to. Also, I will be pretty upset if we never get to visit Kezan/Undermine as an actual zone. I don't like the goblins enough to desire an entire expansion revolving around them (though I do like the goblins), but having a major racial homeland never actually available in the open world is a travesty as far as I'm concerned, no matter whose it is (Gilneas is empty but at least it's there).
I don't accept it because Warcraft has already done it twice. One of the major plot points of Warcraft III was "there's a mysterious land across the seas that has been lost to time since the Sundering because the Maelstrom prevented anyone from stumbling upon it by accident". Then Pandaria was "a mysterious land that's been lost to time since the Sundering because the Mists prevented anyone from stumbling upon it by accident" and even repeated a lot of the same story beats. Doing it a third time would feel like they're just parodying themselves and not even trying to avoid pulling retcons that make us incredulous anymore.
What excuse could be left that we didn't know this place existed after using scrying magic, seeing the planet from space, and having a space ship the draenei can fly around at will?