This will need https://issues.redhat.com/browse/MCO-1806 to land first. Once the updated API has been pulled into the MCO, the controller can begin to listen and update the ControlPlaneMachineSets. Much of the update code can be leveraged from the existing implementation, so this will be more of refactoring. 

With respect to the on-by-default behavior; the configuration injection will have to be updated such that any platforms supporting on-by-default for regular MachineSets will also have the same behavior for ControlPlaneMachineSets.