Are CO2 emissions really a concern? If 5000 of these planes were flying, as a proportion of global CO2, it would be undetectable if they reduced the plane's emissions by 50%. Then you'd have the argument of how much of that CO2 had any measurable effect on climate -- and that would assume that effect was deleterious. A lot of assumptions to bet a revolutionary aircraft design upon.

Adding CO2 reduction engineering to an already difficult project means less resources available to actually get the thing to work.

Imagine if The Apollo program had to worry about CO2 emissions on top of just trying to get a rocket to launch.

You also could argue some economy of scale efficiencies. If one flight on this plane caused just 3 passengers to forego a private jet trip for the same distance, you'd save 3 private jet's worth of flights. Given the time savings, this project would certainly disrupt a segment of the private jet market.

A 777 burns 1680 gallons per hour with 365 maximum passengers. A Gulfstream G650 burns about 865 gallons per hour.. holding a max of 18 passengers. So the G650 is burning 48 gallons per hour, per passenger while the 777 is doing 4.6 gallons per hour per passenger. We're assuming fully loaded for comparison but we all know that a G650 is rarely flying a 18 pax capacity, generally it's in an 11 seat configuration.

So as you can see, even if the fuel efficiency were half of a 777, it would still be a massive efficiency compared to a G650 and thus a net gain for those concerned about CO2.

If 1969 the planet would have been at stake because of CO2, it would have been better to not fly to the moon but rather use the resources to save the planet.