Yeah, you do know that original WOTLK is when store mounts were started, right? The celestial steed came out as the first store mount and it was in WOTLK. So, yes. Blizzard will putting store mounts in the game in WOTLK Classic because they did that with original WOTLK.
You do know that we will be playing WOTLK on the final patch, right? DKs were really bad in the last patch. So if Blizzard left DKs alone, then there will be no problems with them because they are kinda terrible