Stopping the allowance for those living out is not going to happen....maybe jut maybe if renting...but not mortgage holders.
Ending opting out for current and new joiners - more likely being looked at.
That said I know more than a few who are waiting to move into one and two bed rentals for reasonable price,once kids are off to college, so as to help pay for said college. If this option is not available it's sure to lead to more resignations.
It would be another short sighted, quick fix, 'shoot yourselves in the foot' move.
Based on that alone - it's sure to happen. It's the only way they know.