Electric Props
Electric props have been around a long long time, on air transports from the 30's and 40's and even on GA planes like early Beech Bonanzas.
The most infamous was the Curtiss C-46 "Commando". An electric motor was used to alter the angle of the prop blades. With a little corrosion, the electric contact could be lost, resulting in the prop moving into fine pitch and the engine over speeding. This was particularly serious on take off from high altitude fields. They got a bad reputation, needless to say. Today, the FAA will not allow Curtiss Electric props on anything. The C-46 was called the widow maker for the props. Now today's electric props on your RV are not going to be as critical, but on a twin, one engine at full thrust and one at idle at a critical phase of flight could get ugly fast.
The 1940's Beech electric prop had good service, but of course electric props went away in favor of Hydraulic for a reason.
I would disagree that today's electric props are near or on even par with hydraulic ones or super reliable. You use an electric prop because you have to.
Hydraulic props are better in almost every way, especially maintenance, cost and response time (ie RPM control). The same electric prop problems of yesterday, still exist today to some extent. Wires, slip rings, small motors spinning in a hub, all have some challenges operating a prop on planes.
The twins I flew freight years ago had HOT PROPS. The heat elements and slip rings and where always doing weird things. The mechanics cursed them. We flew in known icing and had to have them working. The hot props worked, but it was another thing to go wrong.
Hydraulics, once set up are pretty bullet proof if you don't have a hose leak, but it is a possibility. Lycs had aluminum gov lines and fittings up till the late 80's. There where a few aluminum tube gov line failures, that caused engine failure due to loss of oil, so the FAA let an AD fly, replacing all lines with flex lines or stainless steel lines / steel fittings. After 30 years they decided the aluminum tube and fittings where not good enough. I had to replace two of them on my old twin. It was a pain and about $300-$400 in parts.
It was not the ridged aluminum pipe or fittings fault as much as mechanics who did not reinstall them with the proper clamps and supports. Fatigue took over and cracks happened. Nothing is perfect. Everything has pros and cons.
Bottom line electric props are a compromise, but its also a needed compromise with most auto engine conversion. It's all about compromises. There is no need to deny the limits, they are there and probably always will be with electric props. Aerobatics is not the Selling point for Elec props, nor is the wires and controllers. Also electric props COST more...... So the money you save on your alternative engine will be partly or completely eaten by the prop.