If Bethesda adds in dragon mounts, it would make half the dungeons and quests simple. There are certain shouts and objectives at the top of mountains that you have to traverse through a dungeon to get to. Also the game would have a hard time trying render the frame rate it would take to fly over the entire map, Dragon Mounts should only be a mod.
Just give me the option to ride Odahving. He let ya do it once for the MQ lol. And i'm not saying make dragon that crawls around on the ground. Land or fly should be your options, with a strafing breath attack that has a cool down timer while on the wing. Straffing land bound targets isn't as easy as you think.
So would i love too fly around on the one loyal dragon companion I've shouted into submission? Sure!
Am I likely to see it in Skyrim? Probably not. No.