Clearly Zovaal is a good guy that was betrayed and locked by his power hungry "brothers'
I strongly doubt the sepulcher refers to the Sepulcher of Knowledge.While in Oribos you can listen in on one of the Opulences (the leaders of the Brokers) discussing with their attendants about the crisis in the Shadowlands. The attendant mentions the sepulcher and he is immediately stopped by the Opulence, suggesting they know of it and that they do not want anyone to know that they do so.More importantly when they mention it, it is not capitalized. This suggests we are looking not so much at a location that happens to be named a sepulcher but rather at the burial place of a specific being.
With all the information at our disposal right now I really expect next raid to be against Kel'Thuzad in 9.1, and then focus on Sylvannas and the Jailer (at least 9.2 then 9.3, depending on where the story leads). I guess a small raid againt the Drust to close Ardenweald storyline during 9.1.5 or 9.2.5 could be a possibilty too.What makes me wonder is why Devos would align with the Jailer as at first she fears the power of the Maw from Uther, which makes her legitimately question the order of the Archon, but in the end she falls for the Jailer...I agree also that Ursoc would have been dead before the break of the machine of Death, or he would have gone to the Maw instead (or the Maw still doesnt drain 100% of souls even after the break of the machine of Death ?).