Extreme hybrids are technically feasible:
 

Extreme hybrids are technically feasible:

https://autos.aol.com/article/_a/extreme-hybrids/20051214142009990007

I've seen those
 

I've seen those systems before. There's a small group that has developed them for the prius and escape hybrids. I think they are testing them on fleet hybrids. The biggest downside is the $8k price tag.

https://www.calcars.org/vehicles.html

https://www.evworld.com/electrichybrid.cfm