Reminds me of https://en.wikipedia.org/wiki/V%C3%A9loSoleX:

*“VéloSoleX is a moped, or motorised bicycle, usually just referred to as 'Solex', […] originally created during World War II and mass-produced between 1946 and 1988, came in various iterations, while keeping the same concept of a motor with a roller resting on the front wheel of a bicycle”*

This powers the back wheel, though. I think that’s better for propulsion but it seems you’re giving up carrying stuff or a child on the back of the bicycle. Can’t even have a rack there with this contraption.