Something I’ve identified is that the last expansion tends to have very little exposure in the current expansion.
Mists of Pandaria was almost entirely irrelevant to Warlords of Draenor. Not a Pandaren in sight, not a single reference to that old Horde-Alliance war, hardly a monk around at all. Then suddenly, around Legion, we start getting a bunch of references to the expansion, reminders that it exists again and even chances to visit Pandaria again.
Warlords of Draenor was absolutely not spoken of, when it comes to Legion. It was a reason for Gul’dan to be back and that was it. Not a peep about orcs from another dimension at all. Then with Battle for Azeroth, suddenly it’s no longer taboo to mention the expansion and in fact, we get an entire allied race based off of the expansion, to the chagrin of a lot of people.
As for Legion, well. What evidence do we have that Azeroth was wracked with a horrible demonic invasion only a year ago, in the setting? None at all, aside from a sword sticking out of Silithus, and that’s only relevant because of what it’s doing to the planet right now. The ramifications of the Legion expansion are horribly absent from Battle for Azeroth, but I’ll bet we’ll get a look back at them in the next expansion.
So this leads me to believe that in the next expansion, Battle for Azeroth will be absolutely ignored and its existence shunned, only for the expansion to pop its head back up again in the expansion after that. Perhaps tensions left over from the Blood War will boil over again, perhaps there will be a brief moment of Zandalari or Kul Tiran relevancy again, who knows.
All I can say is that Blizzard seems to hate mentioning the last expansion in the current expansion.