"In the early days of desktop computing the PC was expensive enough to make this a possibility - but the network wasn't up to it."
Eh? In the early 80s, my DEC Rainbow had Ethernet access to the VAX cluster ... Granted, you had to reboot the machine into terminal mode (VT102 if I recall correctly ...). Prior to that, in the late 70s I had an TokinRing connection to the WAITS machines at SAIL in my dorm ... of course the TokenRing terminated at what we would today call a "router", from which I had access to many other campus computers. And prior to THAT I had access to misc. computers at Berkeley via arcnet ... It took about two weeks of hacking to get the hardware to work with my Heath H11-A :-)
"No need to install apps or backups - I could check for details of emails that I'd sent two years ago and forgotten, and catch up with what my students were doing on their eLearning course."
I was doing that with a Panasonic Sr.Partner "luggable" in 1984ish. From there, I had telnet access to anywhere the Internet was ... The difference is that I was dialing into my own "home cloud", which in turn allowed me out on the Internet ... My "home cloud" still exists today. It's grown a trifle in the last 25 years, but I have never had to trust other people with my data while on the road ... Today, I set up corporations in a similar manor.
It's true that in the early days it was all text, but the concepts are the same. And one could make a case for most of what is truly valuable about being connected is text-only.