I hope you realize that both Honda and Yamaha are working on an electric start for there motocross bikes. The only holdback so far is getting a battery that is light enough and has more than one start in it. Doug Dubauck already has an electric start kit available for the YZ450F motocross bike on his web page, Dr. D Racing. If you have ever crashed during a moto on your CRF450 or YZ450F motocross bike and tried to get it restarted you are just about guaranteed to DNF. Me personally I'll take the electric start on a racing 4-stroke.
2000 Honda 400EX
2002 Yamaha Raptor
2004 Yamaha YFZ450
2006 Suzuki Quadsport 50