If you're going to offer a kit to convert motorcycles, it needs to fit as many different motorcycles as possible and make the conversion as easy as possible. The best way to do that (IMHO) is to offer a hub motor, like enertrac does:
EnerTrac
Once you go with a hub motor, then most of the mechanical headaches of mounting a motor and matching the chain drive go away. It just becomes a question of where to put the batteries and the controller/bms. Perhaps you could look into doing a kit based off the enertrac? (buy them in quantity perhaps from the builder at a discount, and then package them up with the rest of the necessary components at a price around $2k... seems somewhat possible...)
Eric