Will the cabin crew "pilot supervisor" stand near the door waiting for the other crew member to return, or take a seat?
If standing near the door waiting, and severe turbulence is encountered, the cabin crew "pilot supervisor" will have to be seated with a seat belt fastened. In some narrow-body types if the jump seat is used, this will physically block the entrance to the flight deck - and the outside crew member will not be able to get back in as they will be physically blocked from entering.
So the outside pilot (could be the captain) will have to sit at a cabin crew station, or a nearby pax seat with a seat belt on waiting for the inside pilot and cabin crew member to handle the severe turbulence event. If it's severe enough, and with an inexperienced pilot stuck inside, it could result in a jet upset - with the captain stuck outside saying Hail Mary's, and thanking Warren Truss (who has no idea, and no experience in anything aviation related) for putting them all in that situation, while the aircraft is spiralling towards the ground with possibly an inexperienced cadet at the controls trying to remember the jet upset recovery procedures while under the pump.
This might sound far-fetched, but it's possible. Did they consider these type of scenarios as part of their knee jerk reaction new procedures??
Probably not
This is certainly a degradation in safety.
How many passengers does a peak hour city train have onboard with only 1 driver, who may be pissed off with his whole world??