Something I saw on an ebike recently. They had exchanged the sprocket for a toothed pulley and ran a belt from the pedal chainring (beltring???). Internal controller give electric assist type throttle and automatic gear shifting with I'm assuming is an internal planetary gear system. Interesting. Also has a battery and rack to complete the system. Just bolt it on, plug it in, and ride.
https://www.sram.com/sram/urban/products/sram-e-matic
