Well, it is forced-air-cooling and the fan won't stall when the motor stalls, so it seems to be quite genius of a design. However, I haven't tested it.
The only problem I see is that since it enclosed the CIM, I think it may block off the radiation waves (don't be scared of that
), to cool down. I think that might make it less effective in cooling itself down.
CIM's don't necessarily run too hot. Our drive motors don't have heat sinks. I haven't seen a single one overheating. However, that could be because we are using mecanum so the motors keep moving even if the robot is stalled, another pro for mecanum!