Yes I realize that p/s boxes are designed to still work manually in the event that the p/s pump fails, but they tend to be harder to steer then even a straight manual steering box when this happens. They are meant for emergency manual use only. Should you shut off your pump at high speeds steering will be extremely hard at best, needless to say a great way to get into a accident.
Granted. However, it would be no worse than losing your P/S belt unexpectedly. P/S boxes are harder to steer because they a usually a higher ratio than a manual box.
When I was a kid, I would borrow a friend's old pickup, which had lost it's P/S pump and never had it replaced. It was a bear to steer at low speeds, but it was fine on the highway. I would certainly use great caution when initially turning off the pump, but the idea of reducing assist at high speeds is one of the things that I like about electric steering. My Jeep is too easy to steer, by my standards (but then I drove a '74 Brockway road tractor with manual steering, so my tastes may have been affected by early exposure to very stable steering.) Ideally, the proportional steering control would be best, and maybe the fellow at the electric Cherokee website will post a circuit that will control the pump.
By the way, Flaming River makes a pure electric power steering (no hydraulics) for their aftermarket steering columns & boxes. Way too pricey tho; mainly intended for the high buck street rod crowd.