Among major European airlines, the practice has been (de facto) in effect for MUCH longer than five years. BA may be lagging behind, in fact.
To reiterate: It's NOT a safety issue, at least in any measureable accident rate statistic. Among aircraft that didn't make it to a safe destination because of propulsion issues, NONE have been four donks minus one. Fuel exhaustion (I mean EXHAUSTION) is a more significant statistic, and that's independent of the number of donks. Even so, we haven't seen a ditch for decades (hijacking excepted).
It IS an public expectation issue, however, and some form of education is in order.