> but once it's proven safe they can get approval to fly over land

The prohibition on supersonic airliners over land is about noise, not safety.

When Boom was first posted here I recall the narrative also including a lot of drag dynamics that would reduce the "boom" which would allow for more feasible overland routes / less noise pollution. Not sure where that sits now - I don't see it as much in their PR copy.

It's still their plan, AFAIK, but the regulatory hurdles to let them do it probably means it's a lot further off than overwater flights.