You must be kidding
*Everything* in this article is wrong.
My MacBook is much easier to use for a normal person than the systems I used at MIT in the 1970s. If you told someone what it was like to use MIT's ITS (Incompatible Timesharing System), they'd think I'm making a (stupid) joke. To login as "ota" you'd type "ota$u" -- no password required. And then you were logged into the DDT debugger instead of a shell. The whole thing was written in PDP-10 assembly.
The differences between these languages is invisible to me -- Dylan looks like virtually every object oriented language I've ever seen; it's hardly amazing.
"Rich file systems, with built-in version tracking, because hard disks cost as much as cars: gone. Clustering, enabling a handful of machines costing hundreds of thousands to work as a seamless whole? Not needed, gone. Rich built-in groupware, enabling teams to cooperate and work on shared documents? Forgotten. Plain-text email was enough."
*Seamless clustering* in the 1980s? What planet are you talking about?
Rich built-in groupware? I have no idea what you could be talking about. Certainly Xerox Altos didn't have that, and they were the most advanced systems from back then. PDP-10s didn't even have a GUI, and the less said about the user experience on OS/360 the better.
People loved Lisp machines because they were some of the first systems that had a GUI at all. You had to program them in Lisp, which, in case you missed it, was a pretty unreadable language. It had some clever parameter binding rules that let you create closures, but otherwise it was a pretty low level language. C++ typing is much easier to use. Modern programming languages exist to help large teams to work on the same projects. You need clean interfaces with enforced module isolation and modern C++ versions exist to do just that.
Editing the operating system you're running as you're running it -- what could possibly go wrong?
"Firstly, because the layers are not sealed off: higher-level languages are usually implemented in lower-level ones, and vulnerabilities in those permeate the stack."
No, sorry, C++ compilers are written in C++. I haven't heard of a high level language compiler written in assembly for decades.
You want some good system design advice from that era? Here, read Butler Lampson's Hints for System Design. It's on the web here https://www.microsoft.com/en-us/research/wp-content/uploads/2016/02/acrobat-17.pdf Lampson seems to think that virtual memory is much harder to deal with than it is, but aside from that, his advice has aged well.