[gnarlysasquatch]

Can anyone positively confirm any OS that handles the scenario described here seamlessly?

It seems like a rare use case that, while feasible, is totally unsurprising that it would require a good bit of research and manual intervention.

[n0rbwah]

I think linux would do fine. As long as the different hardware you want to run it on is compatible with the version installed on your external disk. Which wasn't the case here apparently.