I'm betting the "hearthstone promotion" will be revealed in blizzcon. you sign up for WoW for 1 year and you get guaranteed hearthstone beta + a hearthsteed.
Probably a reward for signing up for Hearthstone within X period of time, or even at all.
Kinda like how if you get an Authenticator you get a corehound pup.
There is a thin line between not knowing and not caring, and I like to think that I walk that line every day.
---------- Post added 2013-04-09 at 03:49 PM ----------
The only real courses that make a lot of sense at this moment are sign up and play during the first few months or a special Blizzcon reward.
Considering the game is free or you've gotten the Blizzcon reward for just watching it online every year; I don't see how people can have an issue outside having it dropped in their lap. Which if it's the former - It will be.
This will probably be something very similar to the CE promotions; A cute little "bonus" for people who play across the Blizzard universe.
-- Signature by /the/ Crazytaco --
Maybe the selling point will be: 'This horse does not have wings, so it does not make an annoying sound while flying around!'