Thus the only way to play as High elf, is for Quel'thalas to go neutral. Or maybe the Horde should get a human faction that's not part of the Alliance.
With the way Pandaran are introduced, this is almost a non-issues now. There are more differences both genetically and culterally between Quel'dorei and Sin'dorei than between the playable Pandaren, whose only difference is a martial philosophy; Judo vs. Tae Kwon Do, if you understand my meaning. Where as Quel'dorei resisted Fel corruption, and have chosen NOT to ally with a countless list of former enemies, namley Orcs (multilple wars against), Forsaken (many of whom propably participated in the slaughter of Quel'Thalas), and Trolls (the most ancient and hated enemy of the Sin/Quel'dorei). I'd say that's fair ground for differences.
I say genetic for simplicities sake because I don't know a better word to refer to the fact that fel-corruption is fairly permanent and passed through bloodlines. I.E., Orcs are still green-skinned after generations, just as Sin'dorei will retain their green eyes and paler skin. These differences will only become more pronounced for Sin'dorei who continue to partake heavily of fel magics.
Even if they did become playable, modern High elves themselves actually don't use magic that much. Just place them in Stormwind.
Dalaran is bursting to the seems with Quel'dorei mages. And their position within the city and Kirin Tor has only improved since the expulsion of the Sunreavers. In addition, the "neutral" Quel'dorie (I.E. those more loyal to the Kirin Tor than to the Silver Covenant) have been brough resounding back into the Alliance fold because of the Sunreaver betrayal.
Even besides Dalaran, a fair numbers of mages exist in Stormwind, and presumably Theramore pre-destruction. The mage tower in Sw has one, Elsharin, and Theramore's portal trainer was Quel'dorei.