If Boom is able to come out with a new supersonic aircraft, is it possible for a startup to compete with Boeing or Airbus in subsonic aircraft? Either coming up with a new design or another innovation that can compete. Or, are those companies pretty much set with impassable moats?
Unless Boeing or Airbus screw up financially, which is almost impossible, the duopoly is set in stone. It will take massive government backing to change that, Airbus itself is proof of that. The only parties that do challenge the big two on single aile jets are Bombardier and Embraer, one of which was bought by Airbus and one which was almost bought by Boeing.
There are already new companies doing short-distance electric passenger flight. These companies could well scale to longer distance flights.
You could also imagine a company like Tesla getting in that business as well.