No load when turning? The alternator has to generate the current to support the motor - when you load the motor, you load the alternator. So either way you take power to run. Contrary to popular myth, the more load that gets pulled from the alternator, the harder it is to turn it - the more power it takes from the engine. I suspect it will take quite a bit more motor/current/power than you think to turn the power steering pump. Do a bit more research - the pressures on the high side of the pump are quite high. I've seen estimates of anywhere from 3 to 10 HP for power steering pumps - convert that directly to current requirements and you get 170-500 Amps - in the same range as the starter. Get ready to hang a starter-sized diesel truck alternator on that puppy.
One thing you can count on - if there were big benefits in terms of costs, reliability or efficiency to run the hydraulic pump electrically, the oem's would've done it by now. And the electric power assist systems being studied/offered that I've read about don't use an electric motor to drive the pump; they use an electro-mechanical rack - like a big solenoid. The steering wheel simply turns a sensor that tells the rack how much to move - "steer by wire". You asked for opinions. I like that you're always thinking outside the box about things and aren't afraid to put the ideas out there. I also think this one's not worth pursuing much further.
Of course, you will have to see what kind of electrical load you'd be pulling and may have to do some modding there (140A alternator and such). There was some talk a while back of some of the newer cars going to 18-24v systems.
