First, I'm not critiquing what Alan or his guys do with this comment - what anyone else does has no bearing on my understanding of wing chun and if it works for them, more power to them
That said, you bring up a good point - that this is mainly an emergency action found in BJ from a WC perspective. So IMO, this is really a
last ditch recovery effort we use mainly because someone got into our space, we lost structure and/or facing and we have no options left, not a WC bai jong ready stance - regardless what type of fighter we are facing. Sure, people can fight from any position they chose. But fighting from a stance where both hands are held in close to the body/chin, you lose a lot of your ability to apply some very key basic wing chun fighting principles.
First, you have no 2 lines or offence/defense and you lose ability to occupy space on center which is essential to WC's Jeet Kiu ideas or applying WC's gate theories for defense (4-gate) or bridging engagement strategies (6 gate). Also, you're are giving up range and timing which you'll just have to recover. Basically, you're putting yourself in a recovery timeframe right from the start. While you can fight from this stance easily enough, and many arts do - doing so it makes it quite a bit harder to apply WC's engagement & bridging strategies from a
wing chun SNT concept/principle perspective.
I'm not saying someone should just stand around like a 'mo with your hands in a static bai jong ready stance either. But from a wing chun principle perspective, BJ emergency/recovery methods are the
last place I want to be, not a position to start from.