An interesting and relevant thread. Thanks to the OP for raising the subject.
It would be good to get as clear a position as possible.
The risk, of course, is to avoid the charter horror stories of diverted flights from those consuming the contents of the 1L duty free bottles, while not preventing those who brought on two miniatures from enjoying them.
In any case, BA wants us to pay for the alcohol (and soft drinks) and not have to clear up the bottles and cans etc brought rather bought on board.