Heavily modified Honda Helix - custom streamlined bodywork, tweaks to the riding position, taller gearing to enable lower engine RPM at high speeds. Craig Vetter claims 80-90 mpg at 70 mph (and that might be into a 30 mph headwind), with better results from Kawasaki Ninja 250s with similar fairings.
His goal is 100 mpg at 70 mph and into a 30 mph headwind, while being comfortable, carrying a useful load (4 paper bags of groceries), and being the first choice vehicle in the garage. Depending on weather... yeah, I’d ride that (although I’d want an electrified version with removable batteries - and he has streamlined a couple Zeros with similar fairings, too). The caveat would be parking, but his concept allows for folding the tail beside the vehicle while parked (I don’t think this one has that feature, though).