I think electrics are at their best in the small "park flyer" sizes. There is no longer a good reason to build a glow plane .15 cubic inches or smaller other than the novelty of a gas engine.

As you go to bigger and bigger airplanes, electrics lose a lot of their practicality. They even stop being quiet! You are not going to be able to fly a .60 glow plane converted to electric in the public park or schoolyard either.

When comparing costs, a .40 doesn't burn that much fuel and batteries don't last forever. You also don't need a huge fieldbox for glow engines. A way to refuel the plane and a battery to light the glow plug are the only things you really have to bring along. I have been flying for years and still don't own a electric starter.