QF has a Project Sunrise which did two test flights by the end of 2019 JFK-SYD and LHR-SYD nonstop of almost 20 hours with flight number QF7879 (by a 787-9).
It appeared to be a success.
EK and QR have some ULH flights to AKL or LAX (from DXB resp. DOH) and SQ from SIN to EWR (18 hours). These flights have limited passenger capacity due to they need so much fuel to complete the flight without refueling.
But now in a climate change conscious world where sustainability is becoming important for carriers, this can be an issue as it is more fuel efficient to make one stop and take two more hours to reach the final destination. Moreover, they have to sacrifice passenger seats to save weight and to add an extra crew because 14+ hours is too long duty for a single crew. I think that such flights will be only feasible for well paying passengers (at least premium Y).

What are your ideas ?