They ought to program a new standard setting for servers, to adjust the maximum number of players dynamically. The system could do just what they suggest, start out with a reasonable small number and raise it until some bottleneck (CPU, RAM, latency, bandwidth) is reached. It could also account for potentially different resource requirements for different game modes and maps (ie larger maps requires more RAM, thus maximum number of players is reduced). Of course, players shouldn't be kicked by the mechanism.
Advanced server admins still could set their own setting. Of course, that still wouldn't prevent cable modem owners from manually setting a too high number, but hopefully some will use the dynamic setting.
Hey, maybe I should patent that.