First of all, if Alliance gets High Elves, Horde wouldn't get a unique race as a counterpart. Allied race for the allied Race, unique race for the unique race. Secondly, Alliance did already get Lightforged Draenei who are almost literally just regular Draenei - a race that wasn't even in different faction and what Alliance player could have already played before, and the world didn't crumble. Thirdly, the 'Allied Race' feature is exactly for reskins like High Elves - that's the entire point of it. So if you see a problem about Alliance getting an extremely similar race, then you should complain about the entire "Allied Race" feature and not just when it concerns High Elves.