When I first started serious research into EV conversions I was surprised to learn that most converters don't bother with regenerative braking. I think the simple reason is just economics. There are other ways, but to do it well it requires an AC motor and controller, both of which are much more expensive than the DC conversions.
I'm currently not planning to implement regenerative braking in my conversion, but imagining ways to do it is irresistible. I got thinking about hooking up an alternator to the back side shaft of my motor, and it occurred to me that the idea is so obvious that surely someone has done it before.
Sure enough, I found a Chevy S-10 conversion, using an alternator and an air conditioning clutch for regenerative braking. Can't find the name of the converter on the site, or I'd make mention. It looks like a well done conversion, but ambitious. He had to re-wire the alternator to generate the 120 Volts for charging....lots of work.