I think it'd be awesome if they created some giant monster that appears once every 15-20 days. Make it 30 blocks high and give it the ability to destroy your house if it sees you. It could start growling at 100 blocks away, giving the player time to hide.
Are you saying put a dragon into the Overworld? No way! That would make it way to risky to build anywhere but a mile underground. And on servers? What a joke! In creative, or with TMI, you'd be giving griefers the ultimate weapon short of the ender dragon or SPC's "/end world" command. If you want a dragon, move to the end.
The Meaning of Life, the Universe, and Everything.
Red Dragons would be cool, but there just not a good idea. If it is implemented and comes from the dragon egg, I will be disappointed because a lot of people I know use the egg as a trophy showing that they killed the Ender Dragon. Also Red dragons being in worlds would be pretty pointless, if they breath fire and are able to be tamed and rode, think of Multiplayer, all the lag spikes, the destruction....