IMO it'd be simpler just enforcing a minimum player requirement with a disband meter that fills when an FC is below the meter, and depletes when the FC is at or above the requirement, so someone is forced to be at the safe level as often as they are below it, or risk having their FC disbanded when the disband meter fills after about 30 days of being below the requirement.
That change alone would completely and totally halt the FC side of this issue - but like any of the suggested changes to address the FC side of things it's going to cause collateral damage and screw over people that aren't land barons because the land barons have abused the system.