Electric propulsion has been in use for some time now in ships albeit powered by diesel or gas turbine generators so maybe more hybrid drive could be the go or there is the other end of the scale in electric trolling motors. Beefy super version could be interesting. I say bring on electric. Fantastic power to weight ratio, odorless, less components, smaller package size , leave the boat solar charging when not in use , distribute weight of batteries to give optimum trim. Also pod drives as used on tugs have incredible manoeuvring ability with 360 degree rotation available. I see quite a few advantages.