I think the best solution to actually end this all quickly would be to have the Void Elves join the Silver Covenant.
The Silver Covenant is an actual organization with a long history in WoW and a big military presence. So it would make sense for the smaller, more specialized group to join them and share what they have to offer. Also given that the leaders of each group are sisters helps this greatly.
Then you can have Silver Covenant themed options added to the Void Elves and say some of them are in fact Silver Covenant High Elves. Even going so far as to add Paladins and just say they are Silver Covenant who learned some tricks from the Void Elves.
This could be done as simply as some NPCs talking like the ones that added new Class/Race options in Cataclysm or even a quest like Night Warrior that awards you a Silver Covenant themed Armor Set and/or a Mount.
Maybe even some Alliance High Elf themes like Alleria’s Tattoos.
This would solved pretty much all the issues and allow the Void Elves to still be their own thing as a specialized group in the Silver Covenant while still getting all the support and themes of High Elves in the Alliance.
The same thing could be done for more Subraces like Sand Trolls, Dark Trolls, and Wildhammer. And even new groups like San’layn, Tunka, Gilblins, and others.