So you would rather have something that is about equal size (cassette + dock) to a NUC and the need to purchase additional docks to actually be useful? I'd say that the NUC is pretty portable for its size, making this idea somewhat redundant. If I were to carry the NUC, all I would need is a keyboard, mouse and monitor. With this, not only would I have to worry about finding the said essentials, I would have to find an extra dock.
The concept is definitely doable if the dock can be manufactured at low cost and widely available everywhere, not just limited to home and office.
Besides, there are computers everywhere these days. If I wanted the security of my own OS, I could just plug in my thumb drive with Slax or Linux Puppy into any PC with a USB port.