ModelCheck gatekeeper has limited usefulness as currently implemented. Once turned on, there are no options to allow the checkin to proceed if the criteria defined in the gatekeeper preferences aren't met.
Add a preference called "ModelCheck Gatekeeper Conflict Override" that when set to yes would generate an overridable conflict in the event viewer to notify the user that the models checked in do not pass ModelCheck but still would allow the user to check in the content. Most companies would like to allow ModelCheck errors on checkin yet prevent promotion/release of the content later. While it's easy enough to add an expression in the releasing workflow to prevent promotion of state with ModelCheck errors, a checkin warning is more difficult to implement as a customization.