Ok, so, the state of the game we have going into Blizzcon is kind of unprecedented. 8.2.5 will probably launch in late September or early October and we still know nothing of 8.3. By this time in prior expansions, the final patch was either on the PTR or already released (at this point in Legion, Argus was already playable on live servers).
This Blizzcon they're going to need to set time to talk about 8.3 and the next expansion. They also need to reveal the new expansion in a way as to not spoil what happens in 8.3, which could be difficult if it ties in directly with the next expansion.
On the other hand, spoil away because no one gives a shit about the trash BfA story. Not even kidding I'd be more than fine with them just showing a cliffnotes slide in the 9.0 powerpoint reveal thats like "yeah so sylvanas was actually plotting/doing X and Y happens in the final raid." I just want it to be done.