Well we do have Taela Everstride who says “calm yo tatas I’m a high elf, i’m not gonna suck the magic out of you!” So the info we have is that they don’t seem to keen on being compared to BE’s.
They remained in the alliance upon learning of what the BE’s did, so that denotes intentionality, and when the leader of the Outland HE’s went to the Sunwell to allow for pilgrimage, he still remains alliance-sided as we see during the Quel’delar quest chain,
As it stands, the outland elves have simply… remained alliance. Of course many could have chosen to formally rejoin, or have the whole of them do so eventually, but what little we have as of facts obviously points otherwise.