Yes, I understand that. However, you figure that it works for watercooled applications that there would be a way to setup a system that would work as well with aircooled engines. It would probably even be possible to have the fan(s) continue to run after the engine turns off for a specified amount of time or until a certain temperature is reached. On my big Z71 switching to an electric fans "saves" about 15hp on the engine. On that V-8 a 15hp gain really isn't earth shattering. Having owned a 1303 for 12 years I know that even a 10hp gain is a BIG deal on the flat-4.
Basically I'm thinking outloud on this and fairly surprised someone hasn't done this (that I've seen). Of course you run into other problems, like finding the right pully setup to run your alternator without over reving it. That and what sort of shroud setup would be needed with which type of fan, etc.
Example of a fan for a Chevy/GMC