Its not gonna happen.
Motability is a Govt created entity with special tax provisions.
Entering the 2nd hand market would put a lot of leasing companies and garages out of business as it is not a level playing field. Neither is it good for the motor trade who rely on a constant source if low mileage 3 year old Cars.
A lot of garages rely on buying and selling ex mobility cars, it is their bread and butter.
It is all academic anyway, as a lot of mobility customers have had enough of the changes and are jumping ship.