I am surprised that certain loco's have not yet spotted the revenue generating potential here...
Manufacture your own brand "approved" cabin luggage, a snazzy orange colour perhaps, or decorated with fine looking harp. Only this particular brand of luggage will be allowed into the cabin. All other types will have to be checked in and carried in the hold (at a charge of course).
Obviously the "own brand" luggage should be made so flimsy that it would break should more than the allowed weight be attempted to be stuffed into it. This would also mean that the life time of this brand would be fairly short and therefore generate more sales.
You saw it here first......