I was never much into motorcycles, I kind of figured the way I drove cars, I'd never survive motorcycles.
I was a little interested with the idea of cyclecars and thought maybe they would be fun. When my son was around 9, I built him a go cart, we lived out in the country, so he ran around the yard on it and had a ball. The motor wasn't big enough for me to have much fun and my wife was pretty dead set against putting a bigger motor on the cart. I think she thought maybe I would have gotten carried away (which probably would have been correct),
When I opened my welding shop, I rented a building a few blocks from the local creek backwater (we called it the swamp). When the water was low, during the summer, it was like a big kids playground. I threw together a few toys (read that V8 4x4) to go play in the "swamp", but my son and his buddies, that were all nearly 16 at the time, were usually breaking my swamp toys (I'm pretty sure my wife didn't know about the swamp toys), I was too distracted with dirt track racing to get too involved with the swamp toys, so that too faded pretty fast.
For a few years, when the price of gas was high, I played with custom bicycles and 3 wheel cycles (I actually built and sold a few of them), motorizing some of them crossed my mind, but that fad passed as well when the gas prices started dropping.
I think putting together a 4 cylinder low buck toy might be fun, but then I wonder where I would be able to play with it and then the story ends again. I can just put gas in my coupe, or my pickup and actually drive them.