Pitchers aren't bred at all, haha.
That would be an interesting thought though. Get Jenny Finch together with Justin Verlander and have babies that can throw 100 mph both over and under handed.
I think the innings thing is hard to argue. You don't really know what would happen to a guy like Felix Hernandez if they gave his arm 250 IP starting at age 20 and then running him up to 300 by the time he's 25. Some guys can handle it, like Clemens or Maddux, but I don't know how much that has to do w/ the fact that they were "bred" that way so much as it has to do w/ the fact that they have flawless mechanics.
Among young pitchers, for instance, I would think a guy like Felix would be more prone to arm troubles the more innings you put on him due to his delivery. Same for Jake Peavy, who has a pretty stressful delivery (he'll have his Pedro Martinez-type shoulder problem sooner or later).
Then again, a guy like Chris Young might really be able to throw 300 innings a year b/c he has low-strain mechanics. Oddly enough, he's never gone over 200, so he's been treated very carefully after returning to baseball from basketball. I think he's an example of a guy who wouldn't be hurt by more work, 7-8 IP a start for sure, 110-120 pitches.