
The point I was trying to make, is that if the device is sold and the consumer is the one with physical access, the device should be treated as compromised. You are correct about minimizing attack surface and blast radius.
The thermostats EOLd before the 20 or so years is more directed in breaking the trust/expectation of the consumer/client. No one reads the EULA. It’s a deep can of worms.
You are correct that the device still works, excluding the cloud services, not denying it.
I don’t think you should be downvoted tho. Reasonable and correct opinion from a (guessing) security professional.
The 20 year smart devices argument should be the norm, imho. We have way too much e-waste as it is. Although that would also mean that smart devices should include that in sales calculations.
The firmware flashing before EoL brings a tear to my eye from the elegance of a solution. Also manufacturers would have to stop with other anti-consumer practices like serialization and scrubbing identity markings, otherwise reversing could be too costly.