Dual-specialization wasn’t introduced until WotLK and yet here we are.
OP, there are at least a few of us asking for this for TBC Anniversary (or whatever we’re calling it) myself included but there’s been no word from Blizzard one way or the other. I don’t see the issue in adding it as I am confident there are many who would throw money at Blizzard with a smile on their face, myself included. Gotta have my army of spacegoats. Just keep asking. Perhaps they’ll listen.