The Horde stuff seems plausible, but the Alliance stuff doesn't.
I can buy some kind of internal conflict between the leaders but what's described sounds really forced. The leaders of the Alliance, by and large, recognize Sylvanas is the problem. Genn has a whole arc about it in Before the Storm and Jaina goes out of her way to spare the Zandalari in Dazar'alor. The only one I could maybe see fighting it is Tyrande, but even her beef is with Sylvanas.
It doesn't really make sense to me that these characters would continue to push a war with the Horde that they're only fighting because of Sylvanas, after the Horde has expelled Sylvanas, and when their mercy is basically the only reason the Horde even still exists at this point.
Which doesn't mean it won't happen, because Blizzard's writing rarely makes sense, but still.