Okay so we know there is an unannounced feature to be added into this expansion, question is, what could it possibly be?
With recent turn of events in 5.1 and 5.2 Im gonna go ahead and guess "sub-races/new skins/hero race/whatever you want to call it" will be implemented.
WHO?
High Elves and Revantusk Trolls
WHY? and HOW?
-First of all both faction have been around the Alliance/Horde since vanilla, have bad blood (see The Hinterlands), and well, what better time than now to be introduced!? We are at war, why not bolster our ranks!?
High Elves
-We all know what has happened in Dalaran. The Kirin Tor/Silver Covenant kicked the Sunreavers out!
-Their alliance dates back to the Warcraft days.
Revantusk Trolls
-They've cut themselves off from the Amani empire and had an allegiance to Thralls Horde.
-With the Darkspear revolting against Garrosh and pretty much the Zandalari getting even more wiped out in Throne, Vol Jin could form a new "Troll empire" with them. They need to stick together if their race is gonna survive.
In Game
-Reason for joining full time...War, we need YOU!
-Since both races are small population, they could be treated like DKs. 1 per server.
-Racials will be chosen from existing ones.
High Elves
-Starting zone would be the same as Humans.
-Classes: Mage, Priest, Hunter, Rogue, Warrior, Warlock
-Racials: Expansive Mind (Gnome) Arcane Resistance (Gnome) Frost Resistance (Dwarf) Arcane Affinity (Blood Elf)
Revantusk Trolls
-Starting zone would be the same as Darkspear.
-Classes: Mage, Priest, Hunter, Shaman, Warrior, Warlock
-Racials: Da Voodoo Shuffle (Troll) Regeneration (Troll) Blood Fury (Orc) Flayer (Worgen)