I think possibly a dragonling mount might happen. However, making it viable for combat is probably never going to happen. It's not a bad idea, but it's pretty unlikely. Other than lore reasons, that all of that animation looks like a pain in the butt.
First, you gotta account for coding in the dragon itself, and making sure it moves, runs and shoots fire correctly. Then you have to make sure that the models of the player races (four in the case of this game) of both genders all sit and animate properly while on the back of the mount. That's 8 models right there. Then, you have to do all the coding and programming to for the spells and need to make sure it corresponds with the dragonling's abilities. This would be if we were only talking one model of dragon.
Then the writers would have to come up with a lot of reasons for this spell school and why there hasn't been records of mages doing it before. The fans would then start finding another reason to fight, asking "Why didn't you give this sooner? I smell retcon, you greedy jerks!"