In that case you would still need a transmission for the engine which would likely increase cost and complexity compared to the surprisingly simple and elegant

In that case you would still need a transmission for the engine which would likely increase cost and complexity compared to the surprisingly simple and elegant planetary gear transmissions used in most modern hybrids e.g. https://en.wikipedia.org/wiki/Hybrid_Synergy_Drive https://en.wikipedia.org/wiki/Hybrid_Synergy_Drive By using two electric motors connected to a planetary gearset you can replace the starter and alternator, allow for electric drive and regenerative braking, and provide a continuously variable transmission for the gas engine all with a set of constantly meshed gears (i.e. no shifting components).