Add certification standard development, certification (both aircraft and pilots; what differences training will be needed?), and so on and so forth.
Well, look at companies like Rotax, Thielert (not the best example, I admit) and Diamond themselves (Austro) and you'll find that getting a brand new engine plus the surrounding systems (FADEC, amongst others) certified actually is feasible for a not-too-large company in not too much time.
Then consider that the potential savings of an electric engine over a Lycosaurus vs. the potential savings of a Rotax or diesel over a Lycosaurus are much greater, consider that once you have the basic integrated systems certification in place, you can just swap in and out larger or smaller motors, or add more batteries as desired, and consider the environmental angle. It's a great business opportunity, better than that faced by Rotax, Diamond or Thielert. For starters that means more investment money available to go through the certification process.
And as for differences training: the UK CAA already has this covered by introducing the category of "Single Lever Power Control" (SLPC) aircraft, for which they indeed require differences training by a suitable instructor, but no specific exam.
If Adam is right and those nanobatteries are indeed going to deliver energy densities (kWh per kg) approaching that of fossile fuels, for an interesting price from a TCO perspective, then I think the rest of the story (the other components, and the certification of the integrated system) is probably sorted in zero time flat.
Oh, and then we'll probably run into the same problem that the automotive industry is already deeply aware of: where are the Amps going to come from to charge all these batteries? The power grid is going to need a serious upgrade to be able to supply even a fraction of the energy that's currently being consumed by road and aviation consumers in the form of fossile fuels.