Every company has its own criteria for a stable final approach. Are you saying that the original Boeing philosophy circa introduction of the first Boeing 737 in the late Sixties did not address the requirement for a stable approach?
One of the current Boeing requirements states: "An approach that becomes unstabilized below 1,000 feet above airport elevation in IMC or below 500 feet above airport elevation in VMC requires an immediate go-around".
As the discussion is about a visual approach and not an instrument approach, then as per Boeing, the aircraft must be stable by 500 feet. Thus selecting landing flap before turning base on a visual approach as a reason to be stable before being established on final, is not valid. It certainly can cause a problem for following traffic.