Hey look, its the Wiki me and DJay are working on.. glad to see people are finding it on their own :)
The Lore page was copied directly from the Lore channel on Discord. My understanding (and Zimon can come by to correct me if I'm wrong) is that the Etheriam are their own race, not a sub class of the others. They are the closest to pure Etheria. But like it says the 3 other races hunted them to near extinction, which is why they are so rare. So far we have met several Etheriam's in the game, Izanami, Tsukiko, Maeve?, Hell, and most recently Emiko.
Given the events with her (not gonna spoil if anyone isn't that far), I'm sure we will meet others. Especially considering there is still lots of the game left to be developed, there will be plenty of oppertunities for Zimon to introduce us to new Etheriams.