The last thing a command-line terminal needs is a Jupyter Notebook-like UI. It doesn't need to render HTML; it doesn't need rerun and undo/redo; and it definitely doesn't need structured RPC. Many of the mentioned features are already supported by various tooling, yet the author dismisses them because... bugs?
Yes, terminal emulators and shells have a lot of historical baggage that we may consider weird or clunky by today's standards. But many design decisions made 40 years ago are directly related to why some software has stood the test of time, and why we still use it today.
"Modernizing" this usually comes with very high maintenance or compatibility costs. So, let's say you want structured data exchange between programs ala PowerShell, Nushell, etc. Great, now you just need to build and maintain shims for every tool in existence, force your users to use your own custom tools that support these features, and ensure that everything interoperates smoothly. So now instead of creating an open standard that everyone can build within and around of, you've built a closed ecosystem that has to be maintained centrally. And yet the "archaic" unstructured data approach is what allows me to write a script with tools written decades ago interoperating seamlessly with tools written today, without either tool needing to directly support the other, or the shell and terminal needing to be aware of this. It all just works.
I'm not saying that this ecosystem couldn't be improved. But it needs broad community discussion, planning, and support, and not a brain dump from someone who feels inspired by Jupyter Notebooks.