It's really not a big deal, instead of flight crew giving approval to cabin crew who then pass on the OK to ground crew when they're ready, which then starts pax filing through the scanning point...
the approval to board at a set time is agreed/assumed and it's the crew's onus to tell ground crew if they're NOT ready at that time.
Considering the vast majority of departures go to plan and tech delays are the exception not the norm, it's all logical IF handled intelligently. If the flight arrives on time there will be a time that the crew can expect the pax to appear in the aerobridge/bottom of stairs. Typically -20. If late that time will be adjusted by the delay.
It's not about pax boarding themselves or scanning their own boarding passes, it's just about cutting out the delay between when the crew say they are ready for pax and when the pax get to the aircraft.