It will solve itself when a pool is too big. As you know, pools are easily changed. There will always be 2-5 large pools as the incentives is to make a pool with the lowest commission to be larger. But the bigger a pool gets, the lower PPS. People switch to a smaller pool when it's not profitable. Plus if hastate goes down, difficulty will adjust. It's not flawless, but it's a pretty good self regulating system.