Shaft drive has been tried and failed, both 20 and 120 years ago. The angle bevel gears just don't work unless they can be really tight, sealed and lubed. NOT possible on a bicycle because of weight and the wheel has to be taken off often.
Variable transmission has been largely a fail with POOR GI range and huge weight and pathetic inefficiency.
Yup, I call them deFaileurs too. Fine for weight weenies but load them up and the lopsided tension spokes start going pling pling. LOL
Rohloff14 with disc for the WIN for me. Dirty chain and all.