There actually were a couple of posts/articles about the mount (Reawakened Phase-Hunter mount) over the last few days.
First to discuss its inclusion as part of the Digital Deluxe Edition and then again to discuss how its mount speed would work in game.
But I have not seen Blizzard confirm yet how it will work in regards to being available to all your characters. That question has been asked a few times already in several posts, hopefully Blizzard will comment on it soon.