Looks like Sylvanas is on-track towards getting killed or experiencing some kind of major character turnaround. I mean, she buggered off to make a deal with evil Nordic she-Hades, out of personal interest. The fact that she wants to enslave the Val'kyr (who are against the Legion already, if I understand correctly) is pretty damning, even without considering that it's at Helya's request. Taking the already-shadowy ex-scourge Val'kyr is one thing, trying to mess with these ones is another.
The 7.1 mini-raid is going to wrap up the Stormheim story, so it will be interesting to see how Sylvanas is involved there. Maybe we'll actually resolve her plot thread pretty early so that we can move on with the real Legion material, or maybe the Horde's part of that story will be Sylvanas asking us to kill Helya because Helya is mad at her for failing. I hope it's the former rather than the latter.
One easy way to lead into killing or redeeming Sylvanas would be putting her in a situation where she has to choose between getting her hands on Eyir, or fighting the Legion. She could pull a Wrathgate and opportunistically snatch her at the worst possible moment, or she could knowingly let her chance at gettin Eyir disappear forever in the name of the greater good. Both would work, and both put the audience in a position where we can clearly understand why she's doing what she's doing and what her priorities are.