First I limited knowledge of the rim drives and zero personal experience so can offer no help in that area.
Regarding DE drives and generators can offer some semi-educated opinions.
Yes, with the proper controller, the right generator
and power output you can drive a motor
directly off a generator
without batteries but the main thing is matching the motor
and generator. DC or AC motor, DC or AC generator?
How many or how few batteries? Totally depends on how much range you want without running a generator. The problem with batteries is that in a typical cruising boat unless you fill the bilge
and make the batteries part of the ballast it's difficult to get more than 50-60 mile range under power and that only at moderate speeds and moderate conditions. Adding a generator adds complexity and cost to the system. My research
came out to double or triple the cost of a new diesel engine
. So DE only makes sense if you're looking at other benefits, potentially the ones you mention like steerable and retractable drive or in my case, a cleaner, more accessible installation
and elimination of a v-drive that is a real pain.