It seems that Blizzard may have finally heard our cries of frustration on this. From tipster Jagoex comes news of a discovery by MMO Champion poster Gurluas: Apparently there are some skins hidden in the patch that look very much like they could be a new look for Sylvanas. The render Gurulas made actually makes her look a bit like a cross between a gray alien and a Blood Elf, but it isn't a bad look for her at all.
At last check, Sylvanas is still bouncing away like a hyperactive cheerleader on the test server, so no word on whether this is really a change for her. If we're lucky, maybe we'll see our new Sylvanas by Wrath of the Lich King, and we can have a proper High Elven Dark Lady we can all be proud of.