I just had this idea that since Dragons, can chose to be any race they want, means that the Dracthyr is an existing race that we have not meet yet.
They can not come up with a race they do not know about or they have not seen.
Since I believe that is true, we will encounter this race in future expansions, and I assume, since the evokers took thier form, that they are a very ancient race in Azeroth.
They are dragonknin, down there with dragonids and dragonspawn, though doubt they are an actual race. 10.1 story shows why it wouldnāt make sense for them to be an actual race xP