Ok I get that game play does not equal lore, and EVERYONE who played through Suramar - every Horde player as well as every Alliance player - was responsible for saving the lives of the Nightfallen, liberating the city, and defeating Gul'dan... But it will still feel strange, remembering all I went through with them to see them forget all that and go to war against us (speaking for my Alliance toons here).
I guess Highmountain and the Lightforged fit into this category too, but neither feels as strange. Both are clearly connected to races already in those factions, and tbh I didn't find their quest lines as compelling. I don't feel a close connection to Turalyon or Ebonhorn the way I do to Oculeth and Thalyssra. Suramar was, imho, the best zone Blizz has ever done and I will always remember it fondly.
Not something that will keep me from enjoying the game, but it will feel strange.