Currently airline passengers don’t have to pay for their carbon emissions, but I doubt that’s gonna last for much longer (we are in an emergency after all). And I’ve seen elsewhere in this thread that the emissions are likely gonna be somewhere between 5x and 10x of normal sub-sonic flights. The price of this extra carbon emission will probably be something that even affluent passengers will want to skip.
Starting to tax airplane fuel would be an important step towards reducing the CO2 output. Possibly that would trigger a switch to synthetic and carbon neutral fuels.
There will be a global cost scheme for carbon at some point in the future. I hope it will be a simple tax (imposed by each state by some international agreements; although some weird cap-and-trade scheme with limited effect is probably more likely given how governments are behaving) and I wouldn’t be surprised if it is mostly in effect by the time Boom plains are in commercial operations.
Whatever the scheme there will probably not be an exception for international flights (I’m guessing countries will be focusing their efforts on exempting their militaries). The thing is that every industry is going to try to get a discount, and that is simply not possible (we are in an emergency after all). So it doesn’t matter if it only shaves of 0.3% of global emissions (which honestly would be a disaster and not acceptable in the long run). What matters is that all industries (except the arms industry; lets be realistic here) will have to suffer equally for their sustained pollution.
Subsonic flight has become much more efficient, cheaper and when paying for higher class, more comfortable. This is one of the reasons often mentioned for the economic demise of the concorde. The audience willing to pay $6000 on a concorde ticket, could now spend $4000 on first class subsonic with a seat that fully reclines into a bed. They can fly a little longer at night but sleep the whole journey.
Wendover did a good economic analysis of the concorde: https://youtu.be/n1QEj09Pe6k
At least.
Even if you think price is a barrier, think about how many more millionaires and billionaires there are in America and Europe today than there were just 20 years ago.
Tack on our society's rediscovered fascination with conspicuous consumption ("influencers"), and I don't think filling seats will be the problem today that it once was.