[CyberRabbi]

No one else has mentioned this but it’s a growing use case for a few in the retro scene:

These older computers are still auditable from a security standpoint. A pre-486 machine doesn’t have binary blobs or sketchy hypervisors that run in ring -1 that are under the control of a third party.

If manufacturers ever cease to provide general purpose machines, one way for the community to bootstrap itself would be from old hardware or FPGAs (if they can be trusted).