Hybrid minivans

As far as passenger vehicles go, it seems to me that the best ones to hybridize would be minivans.

Minivans usually get worse mileage than cars, so the impact would be greater. Pickup trucks and SUVs obviously get bad mileage as well, but a lot of people buy those who don't fully use them, or, if they do, don't do it often enough. Those people would be better off just buying a smaller vehicle with a conventional power train and renting a larger vehicle as needed. On the other hand, you can be pretty sure that anyone who buys a minivan derives substantial practical benefit from the things it can do that a smaller vehicle cannot. Nobody buys a minivan for image.

The usual owners of minivans tend to be families with multiple children. Odds are pretty good that they do more driving than the average person getting kids to and from school and other activities. It's also more likely that minivans will be in stop-and-go driving situations where hybrids are most valuable. Of all passenger vehicle types, minivans seem like the best target for hybridization efforts, because they use substantial amounts of gasoline, there is often no practical alternative.

Most of this probably applies to smaller SUVs as well, but they're basically just tall minivans anyway.