volvo flywheel
 

maybe somewhat on the edge of the definition of a hybid but still interesting technology.

Volvo shows off KERS flywheel tech [w/video] — Autoblog

there's the weight as space issue, but than again that's much more the case with hybrids too, also the way this is set up, fitting it to an EV is an option.

perhaps this could also be interesting for busses as these are heavy vehicles that are forced to make frequent brief stops, but are big enough to house a large flywheel...

Never going to happen, pie in the sky, volvo needs to get its act together.

(Sigh) Porsche did it last year: Porsche Unveils 911 Hybrid With Flywheel Speed Booster | Inhabitat - Green Design Will Save the World

And of course the Gyrobus has been around for upwards of 50 years.