While doing a little research for something I was writing, I checked to see what information was available on the location that Zovaal and his unwilling sidekick went to at the end of the most recent cinematic.
Apparently the Sepulcher of the First Ones is located in a realm called Zereth Mortis. ‘Zereth’ apparently means cornerstone or keystone, although if you want to really dig, there is a Hebrew translation that means “splendour” or “Perplexity”. Mortis is interesting.
Mortis in Earth history comes from the Latin for ‘Death’ (as in Rigor Mortis). Im not sure why the First Ones would name something after human languages but if it does happen to have the same meaning, then the place Zovaal and Anduin went to is basically called either “Death’s Foundation” or “Death’s Splendour”.
Either way, it rather links in to Zovaal’s plans, especially the “Death comes for the soul of your world” comment.
So my impression is that what we will be visiting is a realm outside of spacetime relevant to both the Shadowlands and our game reality that contains a place called the Sepulcher of the First Ones. And as Sylvanas muttered as she hit the ground, we need to stop him reaching it, assuming we even can.
Since its been pointed out that time works differently in these realms outside living space, we could either arrive there shortly after Zovaal does or way too late.