You can't have an electrical cut-out that doesn't cut-out certain components. The reason you need a complete electrical cut-out is for safety reasons (eg fuel leaks into engine bay). If the ignition switch is not used for that purpose they would need to put a big red button on the dash like GP said.
The ignition switch cutting all power has worked without incident in every other brand for many decades. The issue here is GM's incompetence, and I'm not inclined to the idea that they would have competently implemented another system.
If anything I think this is an argument that power steering should be limited so that average drivers don't lose control of their vehicles if it fails (I've lost power steering in motion due to an engine stall, it is very scary).