Well, Taalva, the issue is that short of introducing a new character (or some how making Azshara a nelf again) you would need to create an entirely new character, and that runs the distinct risk of not wielding the same impact as one players have known since WoW was Vanilla.
It also really would not be making the Nelves that we the players know the victim. This remnant would be showing up to conquer the -Alliance- and Horde. This means -all- of both present. It would be the rough equivalent of a new, different nation showing up, much like the Eternal Empire in SWtoR.