I don't believe there is an endgame planned for them. They're an Allied Race, not a main race. If Blizzard spent more time fleshing them out (in what way really anyway?) then that means every Allied Race that comes out with little lore would need an endgame as well which would then become insurmountable work and effort very quickly.
I think what we know about Void Elves now is pretty much all there. There's not going to be any lore developments with them that somehow is mind-shattering or throws a curveball.
They're former Elves that got doused in Void and now have to control the whispers within them (like Alleria). I can't see what extra developments they could have that adds very much new to that point.
I just believe anyone expecting some WoD level treatment like with the Draenei culture are going to be disappointed when that doesn't happen for Void Elves.