Going beyond the Lagoon system from Solomon Technologies is the Fischer-Panda Whisper Prop system. The electric motor is in a small pivoting pod under the hull just like on all the new ocean liners. Noise is reduced even more and it's a simpler drive system without the thru-hull prop shafts. Also the motor is efficiently cooled by the surrounding water. I believe that system is available on Bavaria. Think of a trolling motor on steroids. Plus since it pivots you don't need a bow thruster as much.
These systems are best engineered into a new design where the still heavy large battery banks and electrical cabling can be placed optimally and intergrated with the generator for cruising distances.
On the down side when those batteries start to fail there is going to be a very expensive swap out, just as with the Prius.
Another very interesting player in the market with good looking engineering is Glacier Bay with their OSSA Powerlite generators and propulsion motors. They have a good write up on electric propulsion on their website. Below them are a bunch of suppliers selling battle-bot and wheelchair motors with some packaging for yachts.
For my headstone:
If I'd only listened to those guys about that wing keel...