There's not just one, but
two threads covering the same question by the same OP: http://www.gamesas.com/topic/1327494-dragon-riding-in-a-new-dlc/
It's mindblowing!
Here's what I put in the "other" thread:
I'd rather not.
Spoiler Even though we have the ability to see it firsthand (although as a cut scene), I'd rather not see it as a full time feature.
Not having winged mounts is one of many things that separates the ES series from WoW. If you really want this to happen, go mod it yourself and have fun. Nothing's stopping you from enjoying your single-player experience the way you want to.