Though not limited to B6, this is generally a fairy annoying trend for all sorts of reasons (not least of which is security issues...there have been too many "outbursts" of airport security going horribly wrong, for example). Unless I'm getting a free pre-takeoff drink, all else being equal I'd really rather wait in a terminal (where as often as not I have wifi and so on). Moreover, as noted, there's one issue of more time being carved out (e.g. boarding door closes at 2044 for a 2059 departure) and another of a "final call" at 2024 (a full 35 minutes before departure). Especially if takeoff generally cannot be expedited, I really do not see a value to the pax in forcing another 20 minutes of advance-arrival time at the airport.

FWIW, even Amtrak is moving in this direction (though to be fair, I think the ten-minute reservation cut-off at a handful of major stations has more to do with not wanting panicked pax running through the station).