Okay, so my friend Cal came up with this idea, but asked me to post it because he hasn't made an account on the Minecraft forums yet. All credit goes to him for this:
I have a serious proposition for a future update for the developers of Minecraft to think about.
You know, I'm sure of the idea that was leaked out and rumored to be added in 1.7: the Red Dragon. However, the Dragon never came to reality and this is disappointing.
In my view, Minecraft should strive as much as possible to add more mobs and created structures. This aside, I am a HUGE fan of your game and I hope you will keep up the good work making this amazing game better.
My proposition is as follows: In a future update you should add the Red Dragon, which spawns rarely and in Dragon Lairs, caves in mountainsides, where the Dragons come out of and fly within a certain radius at day or night. The Dragon would either be Aggressive or Neutral; if Aggressive the Dragon would have treasure behind it in the lair; if Neutral, you would have to kill it to get treasure. The Dragon would have damaging fire breath but the health would have to be much decreased from the Ender Dragon. The Red Dragon in my view, should NOT be a boss mob, but only a very powerful one.
Last but not least, I propose that Red Dragons be TAME-ABLE and RIDE-ABLE with a saddle crafted out of a valuable material. Don't take this the wrong way; I want the process of taming the Dragon be VERY DIFFICULT, especially if the Dragon were aggressive.
Anything involving the words "dragon" or "tame" is going to be attacked on these forums because the idea has been suggested 217 million times and in almost every instance, the word "overpowered" is tossed about. You have been warned.
Pertaining to the actual suggestion, it is a little vague. We need more details, like how to craft the saddle, how much health does the dragon have, how much damage does it do, what are the flight mechanics, and so forth. Flight in survival is likely never going to be implemented unless it is an alternative, not an upgrade, to walking. That means it has to be so underpowered and nerfed that you're probably better off walking in the first place. I don't agree with it, but that's just the world we live in.
Red Dragon, which spawns rarely and in Dragon Lairs, caves in mountainsides,
Personally, I think that the Red dragon, like you said, should be extremely rare but instead of finding them in dragon lairs or whatever, they should spawn in VERY VERY tall structure like trees with a dragon's nest at the top and that is where you would find them