The Air Force actually does this with avionics. A lot of the older planes require electronic components that speak a protocol that ran on hardware that is not

The Air Force actually does this with avionics. A lot of the older planes require electronic components that speak a protocol that ran on hardware that is not directly replaceable. Instead, they run "emulator" boxes that are the same physical size as the old components and have the same physical ports but run Linux (or some other modern embedded system) inside.