I wish UO taming was like Star Wars Galaxies Creature Handler system, where they have nests of creatures and you have to wait for babies to spawn, so it would be a challange in trying to tame them, getting past the adults to tame the babies. Then the babies grow over a period of time and you can train them special moves as you go along. That would be awesome.
Can improve on that idea with your idea of breeding pets etc too. So much potential for a good taming system.
I love my pet classes, im always a pet class on any game i play if there is one. I think UO tamer is the second best pet class i've ever come across, but the Star Wars Galaxies Creature Handler was just plain awesome.