I don't think it's useful to conflate the terms 'mobile' and 'portable'. You've been able to make a portable desktop for several decades. (I recall one Compaq that came in a closable case with a handle.) That's not typically what people mean by 'mobile'.
That 'extreme example' weighs as much as many laptops and it's just a case. Even if you carried a small display, and everything else you need, I doubt most people would take that out if they found themselves with extra time at the airport.
Edit: Found the machine I was thinking of: https://en.wikipedia.org/wiki/Compaq_Portable
