I have not seen anything in lore where the High Elves have always been part of the Alliance. I have seen they have joined Alliance factions in the past to deal with either the Amani Trolls in there homeland, to deal with the Horde invasion or being part of the Alliance resistance after all of Lordaeron fell to the scourge invasion… So them being an Iconic Alliance race does not make any sense at all.
Giving Void Elves “High Elven” customisations doesn’t make any sense, considering that the Void Elves were transformed by Void Etherals due to there study into the void. Alleria only absorbed the Void Mastery from the dark naruu L’ura.