A number of hotels have been trying this for some time now...not that I've ever see it enforced, but then again I usually don't leave early.
At Chicago Hyatt earlier this year I was concerned about getting out on the Sunday of the marathon, so I asked about checking out early..."Yes, but there is a charge". Things changed fast when on Saturday they were oversold by 200 rooms and were waiving incidentals and giving bonus Passport points to leave early!