Originally Posted by
Yvaelle
I don't think it's fair to assume all of the Broken Isles is with the Horde.
If you were paying attention to the story lines, Suramar was a civil war with half the highborne siding against Elisande and her demons, and working with Tyrande (if the Alliance side of the conflict becomes the canon side) to overthrow her.
Some faction of the Nightborne and Highmountain Tauren (three tribes with differing views too) could end up siding with the Horde and becoming playable, without their entire race joining. Also, the Nightborne are probably pretty fucking devastated right now in terms of population and ability to control the Broken Isles: they were trapped in their bubble for 10,000 years, then the demons invaded them as their first stop, then they had a civil war, then both of the most powerful factions in the world (H & A) both invaded their city simultaneously, killing off pretty much everyone on the assumption they were all corrupted by demons, then we slaughtered their chain of command and took their loot.
The Nightborne aren't a continent controlling faction after TOS, they're refugees with conflicting factions and bitter rivalries that allowed their once-great empire to fall to dust in the span of a couple years. They would pose no threat to the elves of Val'Sharah. Some might join the Horde, most of Suramar might simply focus on rebuilding after TOS. A war with the entrenched Nelves in Val'Sharah wouldn't serve them well right now - especcially because I'm sure a lot of the Nelves are going to be looking for someone to kill - best to keep your head down right now.
As for the Highmountain Tauren, Ebonhorn is pretty important to them, and he's a black dragon - Wrathion has demonstrated he prefers the Alliance (or, would prefer if they win the BFA, circa Pandaria): it's reasonable to assume Ebonhorn may not agree with the Highmountain Tribe that sides with the Horde. One tribe might join while the rest attempt to stay out of the BFA.
The Naga are night elves - and we have our conflicts - but deep down the Naga just wish they were still sexy: they just want to rejoin us. Also, Aszuna is filled with Night Elf ghosts who kill - so it's not going to work out for anyone but the Night Elves to control Aszuna.
Lastly, we know the Vrykul aren't going to side with the Horde - they want Sylvanas dead circa TOS - they'll only be less happy with her now that she is the leader of the Horde. So they will likely be a lot more hostile to Horde factions than Alliance, even if they don't become playable for Alliance.
I think TOS factions are going to be a lot more divided than people initially think just because they have playable horde sub-factions.
Val'Sharah/Aszuna might be the most logical place for the Night Elves to rebuild.