You have to remember that the Hearthstone team is not the same as the WoW team (at least as far as i know) and that they threw some jabs to the WoW team (albeit i do not remember when i saw this).
A worgen tail could be one of them with someone in the HS team wanting it to happen.
But it’s also true that the WoW team take things form HS like the League of Explorers so it’s still possible to see something for the worgens.