Update: New screenshots are coming in from different sources that seem to confirm the new Alliance race is some sort of Eredar-hybrid. One of the screenshots below show this Eredar wearing a Paladin set and a libram chained to him fighting a Blood Elf female.
A fan named Cybsled shared his own fanfic story (speculation) to explain why Eredar would be a digestable new playable race. It would make sense:
“Blizzard’s April Fools joke wasnt a total joke.
I’ve seen the grabs of the E3 video, and the starting area clearly looks like Mt. Hyjal.
My theory: After the wisps all owned Archimonde, they absorbed part of his power/energy/form/whatever. This overwhelming power transformed the wisps, giving them mortal form again in the shape of an Eredar. However, since they have the souls of elves, they arent evil and are accepted into the Alliance on this fact.
This idea fits right in with the Blizzcon statement where Metzen said “At first you will go “HUH?” then go “Oh, that makes sense”.
I remind you this is not official. And the race name and history has not been revealed until tomorow or Thursday. Many fans are starting to accept and assimilate the Eredar-wisp merge speculation.