Flying LGW-Marrakech this week, at the end of the flight the crew apologised over the tannoy for the fact that they had not been able to complete the drinks service in Y (full flight). If they can't achieve this on a >3hr flight, then there's not much hope for them!
I'm guessing BA management didn't stress test their payment systems to see if it would actually work to make the concept feasible on a short-haul flight! They just don't learn, do they!