Marc, just thought I would give you my 2 cents worth... I have not built any airplanes but have been lurking here for a couple of months. I have no idea of the extent of your flying experience and am not trying to insult you. My flying background includes C150/152, C172/172XP, PA140/180, Citabria, Piper Cub, T34C, KingAir 90, P-3 Orion (Electra), 737-200/-300/-500/-700. Out of all of these airplanes, only the 737 has electric roll trim. It is usually set on the ground and not touched the entire flight. Occasionally, you may make a fine adjustment in flight.
Electric pitch trim makes sense to me because pitch trim changes with power/airspeed. Roll and yaw trim don't require that many changes. If I were building an airplane, I would not even consider adding electric motors anywhere that I don't have to. Not only does it add extra weight and complexity, it is also an additional source of fire. The only exception that I'll make to this is that when I build an airplane, it will likely include a two-axis autopilot which will of course require pitch/roll servos.
I just thought of this as I was writing this post. Does a pusher exhibit P-factor induced yaw like a tractor configuration? I would think it is at least significantly reduced.