Such systems should be airgapped…

I can think of two approaches for such companies:

a. Use commercial OS vendors who will push out fixes.

b. Set up a Continuous Integration process where everything is open source and is built from the ground up, with some reliance on open source platforms such as distros.

One needs different types of competence and IT Operational readiness in each approach.

> b. Set up a Continuous Integration process where everything is open source and is built from the ground up, with some reliance on open source platforms such as distros.

How would that have prevented this backdoor?

At a certain scale, "economic" systems become critical to life. Someone who has sufficiently compromised a systemically-important bank can do things that would result in riots breaking out on the street all over a country.

Something that is critical to life should not be connected to Internet.

And yet it seems like every new car is.

Sshhh now you are starting to talk like a rightwinger. Alex Jones has been saying this for a long time ;)

You could use the EPA dollar to life conversion ratio.

Though anything actually potentially lethal shouldn't really have a standard Internet connection. E.g. nuclear power plants, trains, planes controls, heavy industrial equipment, nuclear weapons...

In that case OP should not design systems were a sshd compromise can have a life-threatening impact. Just because it's easier for everything to be controlled from the cloud doesn't mean that others need to feel sympathy when that turnes out to be as bad of an idea as everyone else has said.