"The members of the Dragon Riders have mastered the ability to tame select dragons, mount them, and soar the sky on the backs of these majestic, but dangerous beasts." 
Whoever wrote this just took the things people were most vocal about and threw them all together. Dragon mounts, visiting Morrowind, Cyrodiil and Hammerfell, more shapeshifting, more Thalmor.
Also, has anybody noticed how they propose sabercats, bears and
wolves as mounts? Wolves are small. Bears are just ridiculously unfeasible.
It's no leak, just a gigantic fake.
But if they do release a DLC based around dragon mounts, I'm so not going to buy it.