I think there should be a mob cap per chunk. I don't know what the good number would be, I would say no more than 500 mobs per chunk. There are plugins out there that can be used to do this, I did the research before adding this suggestion. We are having players sit AFK at grinders literally for 6-10 hours at the time and allowing thousands of pigmen to spawn. This lags the crap out of the server causing certain things to become almost impossible without lagging out.
