> If a producer goes out of business they should be forced to give out a signed firmware that disables the key checking, then they must put up their source code for any users who wish to build and flash it themselves.

Requiring an organization to do even a small amount of engineering as it is going under is simply not going to work in practice.

IMHO the only possible way for something like this to work is to require vendors to upload buildable firmware source into a third-party escrow system before you can ship devices to customers.