Carnie: There could. There could be all kind of such rules, and they have been discussed before (about once a year... scroll down.)
In a nutshell, it is not that easy. There are people that have 800 games running, and play all of them multiple times a days. And there are people who have five games and play each one after 30 days once. In other words, the count is not a good predictor of playing speed.

The only solution currently is that you make your own list of 'slow' players, and don't play with them anymore.

P.S.: My preferred idea is that the system shows at each players profile his 'average time to move' for the last 60 days; and that you can chose to 'hide all games and tournaments' where this number is greater than a number you decide.