Could stick a drive on an ExpressCard to NVMe adapter.. I’ve got one in mine, I don’t boot off it, but I believe it can.. Runs a bit warm, but it’s been powered up and running 24/7 for 2 years with no issues..
Very cool! Do you see decent performance with the adapter?
Sounds like a nice setup though. I too have an old laptop that's been running 24/7 for years. Kind of the perfect small server - low noise/heat/power and has a built-in console.