[pete c]

I think I have seen this discussed somewhere here before.

Would an electric supercharger that also served as an alternator make sense?

My thinking is that you might be able to recover some of the pumping loss by turning the supercharger into a throttle by putting an electrical load on it during partial throttle situations. On a hybrid vehicle, this power could be sent directly to the electric motor. I suspect that you'd still need traditional throttle for some situations where good throttle response was needed, but in regular cruising mode the throttle goes full open throttle duties are handled by varying the electric load on the supercharger. An added benefit is that when you ring up all ahead, full, you put power to the supercharger making it into a traditional supercharger.