Sylvanas isn't getting "redeemed" imo but her quest text when you give the blade to her make it pretty clear she knows about old gods and is aware about how their meddling has instigated faction hostility. There can never be peace as long as N'zoth continues to manipulate from a place it cant be reached.
My hunch is that she instigated the war knowing it's the only way to lure N'zoth out. It was never really about the alliance, she just needed everyone to think it was. And now a dagger that has sealed an old god away completely is in her hands...
This is potentially interesting in the 'you, the player, were the unknowing pawn of the big bad' sense, (it's been done with other MMO's before, but not too often with WoW, if memory serves - what's his name in Zul'Drak from WotLK being the first one I can think of), but I feel there's a discrepancy between this type of narrative, and throwing Sylvanas into the cartoon villain spotlight.
Of course, it could be she's taking on the 'villain' role so that the horde and alliance will solidify into a cohesive unit and become the 'dark lady' that brought Azeroth together....but that feels like an asspull too.
What I'm actually really curious on is the 'option' horde players have to keep warning Sylvanas and the potential alternate storyline - so far, both of the 2 instances so far, and the 1 on the PTR, just result in her/Nathanos telling us to 'keep doing what you're doing, it's all part of the plan'.
Like....at some point we've gotta get some actual insight into the plan/motivations you keep telling us you have, unless it's just 'fake it til you make it' - because both options have resulted in Sylvanas decidedly 'not' winning.
The cynic in me says it'll go nowhere, fast, but Blizz has 'hinted' that they'll start offering similar choices for the alliance to have to make, so we'll see.
