Originally Posted by
Caerule
I can see the Red flight go Horde, but only if we get Thrall in charge, and the Banshee Queen is kicked out.
The Orc Clans that enslaved the Red Dragonflight are those of the Dark Horde clans and Dragonmaw. Dark Horde clans never joined Thrall's Horde. Dragonmaw joined, but largely met their fate as Garrosh loyalists. And according to the Shaman questlines in Legion, the Highlands were completely overrun by the Burning Legion. So the Dragonmaw are a limited factor. Meanwhile, the mortal Alexstrasza is closest to, likely is Thrall.
Green Flight has ever held strong bonds with the Night Elves. While Malfurion champions the Emerald Dream, I don't see anything breaking that bond.
Blue Flight is an interesting one. They've been friend and foe with both. As Kirin Tor isn't part of the Alliance, and as they enjoy magic above everything, that should make the Horde a tempting candidate, with all those elves. However, the one obstacle is Kalecgos and his love of Jaina. Also his half-Human avatar. They're just not going to make that guy go Horde, with his baggage.
Black will go with Wrathion. Honestly any side would be crazy to accept him. His flight probably suits Horde more. Wrathion is the obstacle here. He has a clear Alliance-bias. But he's about as trustworthy as Loki. While he might like the Alliance more in principle, that's never changed his actions before. I'm gonna go with "Whichever side he feels like, at the time."
Bronze would be an interesting discussion. Location-wise, Horde seems more valuable. But Alliance has a lot more involvement in history. Personality-wise, I see them be rather structured. Their role is maintaining an ordered system. That seems Alliance. All of those arguments are garbage though. Because Chromie is the most famous Gnome NPC in the game. And so Alliance is the only option.
I don't really see the other flights being worthy of much consideration. I doubt they'd get involved. I could argue how Nether Dragon most suits the Horde. But let's face it, Alliance isn't going to open its door to any of those dragonflights, so if somehow they joined any site, it's Horde by default.