Most people I have spoken to about it do want to move to electric propulsion - I guess it's just down to who you talk to.
For me the benefits seem obvious:-
Travelling along your favourite waterway with only the sound of the water lapping against the boat and the birds singing
No fumes to breathe in when in locks or when the wind is in the wrong direction
Big savings on fuel costs when batteries are charged from solar panels and / or wind turbines
At some point, we're going to have to stop using combustion engines
On a recent demo, the 55' narrowboat I was on was propelled purely by a 10kw electric motor at ~3mph and the power coming from the solar panels exceeded the current being drawn by the motor. Obviously this was a lovely sunny day so this wouldn't always be the case, so the boat had a little diesel generator for our dull weather ( yes I know that's most days 😉 ).
My current thinking is to attach (bolt or weld) a splined pulley onto the prop shaft close to the coupler, then bolt on an electric motor with a suitably sized splined pulley on it's shaft, with a nylon belt driving the shaft. The resistance from the gearbox is very low when in neutral so I don't think this would add much load to the motor when in electric mode, and the motors turn freely when turned off, so equally wouldn't add much load to the engine when under diesel mode.