There is a long history (world wide) of tail strikes occurring, even on the A320, due to inappropriate landing technique being employed by inexperienced pilots. Hence why cadets at EasyJet are not permitted to do Flap 3 landings for the first period of their line flying due to the increased risk of a tail strike.
It is however particularly relevant to the A321. A simple way of mitigating the risk is to say that when the A321 is flown, the Captain is the PF. It really doesn't throw up any rostering problems at all so I don't see why that, in itself, would cost the airline money. I suppose insurance costs do increase if you employ cadets but that is surely offset by the fact they are paid considerably less.
I would be gobsmacked if BA didn't launch another cadet program at some point in the future, but I would wager that a) It will not be in 2016 and b) when it does launch the terms and conditions may be different (worse) than the current scheme.