HD stern drive has all the problems of every outboard or IO drive.
Hundreds of parts all wanting to be a battery.
Jet drives work , but the boat needs to be really fast to get minor efficiency , a displacement trawler with 6K and a fuel burn like a sport fish? UGH!
The shaft and prop works well , why screw with 100 years of success?
Stern drives for diesels are heavier than for gassers as the torque peak as each cylinder fires is far higher .