At the moment things are looking pretty grim for the Horde PC:
If you side with Sylvanas, you are actively snitching on major Horde leaders and betraying their trust. Should the rebellion win, the PC will never be trusted by the other Horde leaders again. That's assuming the PC is not just outright executed after Sylvanas is deposed.
If you side with the rebellion, you are actively committing treason. Should Sylvanas win, the PC will undoubtedly be summarily executed.
Things get even more grim if you take into account the whole Xal'atath / Gift of N'Zoth fiasco. Should you keep N'Zoth's gift, not only are you committing a grave crime against both the Alliance and the Horde, you are also putting the entire universe in dire jeopardy. It is very unbecoming of the "champion" of Azeroth to consort with an Old God.
And even if you cleanse N'Zoth's gift, you still heed his call and give Xal'atath to Sylvanas leading directly to untold casualties in the lead up to Nazjatar.
I think there's only 2 viable scenarios:
1) N'Zoth completely decimates both the Alliance and the Horde and makes the PC his prime enforcer
2) Nozdormu shatters the timelines and resets everything to pre-BfA
As someone who gets invested in his character's story and roleplays a bit, BfA is making me kind of worried. At this point I'd rather hand myself over to Anduin and beg him to absolve me of my sins than continue with the Horde / N'Zoth story.