If this were to happen, what would you as a player do?
Blood Elfs imho are one of the most annoying races in the game, and just plain stupid looking (at least the males are, and their dance is atrocious). The only other race that comes close to how annoying the Blood Elfs are, is the Goblins. Plus, theres not a whole lot of lore surrounding the Blood Elfs to begin with.
If the Alliance were to add High Elfs to their faction, I would want to see them "buff" them up so to speak. Make them larger, more brawn, but keep the females petite and dainty. I like me some dainty females if you know what i mean! Would you like to see high elfs added to the Alliance in the next expansion along with Ethereals?