Glueball,
Maybe they could.
They have had that opportunity in Australia for a few years now.
Precisely ZERO foreign carriers have come in (aside from AirNZ buying an already going concern which subsequently went kaput).
DJ is not part of VS - but there would be nothing stopping it being so.
Anyway... QF and DJ are making good money on pretty heavily-trafficked domestic routes - so if Biman wanted to come , they could, probably pick up some qualified personnel, equipment and slots cheaply and earn the 'hard currency' you speak of.
But guess what? They haven't? And they can't, unless they can convince the local safety authority to give them an AOC.
So it's not a free-for-all.
Or are you indicating a lack of faith in the regulatory system to licence and oversee newcomers??
It is possible to perhaps not see much difference between a properly licenced and regulated Biman subsidiary operating in the US and repatriating 'hard currency' and certain American corporations flogging fast food in Dhaka and then paying out 'hard currency' to their shareholders back home. It's up to the punters to put their bums on the seats of their choosing. If it's good for the goose, mate...