@Bracken_Dawson My preference is to use a single rail PSU. There’s only two ways to wire it, the right way and the wrong way (in which case a polarity-protected regulator copes).
On detecting e.g. a shorted MOSFET, by some means, you disable the broken heating circuit and warn the user. Provision of individual enables for each heater and motor costs more but allows the hardware to continue operating at reduced capacity. In my case I am supporting 5 hotends and a fault on one doesn’t result in loss of all them all.
I agree that users can do stupid things with any solution you come up with but there is more scope for taking dangerous shortcuts when too many requirements are placed on the user e.g. like requiring them to use a PSU with specific functionality.
Two different designers will, inevitably, have individual opinions on how to best achieve these levels of safety. Mine is to simplify what the user must implement and instead require the electronics to manage failure scenarios where it can.