First I considered that 2.3l/100km is pretty great. But when actually scaling it to full car with 4 persons in it doesn't feel that special anymore about 9.1 l/100km. Which really isn't anything to write home about even in larger sedans.
If fuel economy is your goal, you can take a glider.
A skilled glider pilot can go (slowly) as far as they like with no fuel. The typical limit is when you get tired and need to sleep (gliding can't yet be done well by a computer, because it takes quite some skill to find the necessary thermals and wind currents).
Typically it is very hard to glide at night since a large part of gliding is the air movement caused by local and regional thermal differences.
Ardupilot (or one of its offshoots, I can't recall exactly) does have a lift detecting autopilot in beta. I don't know how it works with a specific route, but it seems to lock in thermals pretty well.
Now this is something I'd like to see. A permanent glider, in the sky for years on end. Obviously with humans onboard you'd have to resupply it with food and water.
But with a computer - train ML on human pilot behaviours? - it could stay there for quite some time.
