I probably will happen, the lore supports it.
In the meanwhile the alliance story including High Elfs will probably shift from them to the Void Elfs. Then High Elfs will be added to the Horde, not as an allied race, but as an eye color as there is no visual difference between High/Blood elfs in the lore. Not even the eye color is what the division between High/Blood elf are about, but it has represented it.