I really appreciate you sharing this!
It's a ~90% match for the UI I've been planning for the JSON editor in my "next Excel" tool, and I have yet to see anything similar in the wild.
This is a very early stage mock up of the tool:
http://tableflow.org/studio/flow/#a
The 10% difference would be:
I would handle the nested structure a bit differently. Instead of being visually nested, you would go to an entirely new view and just be shown a breadcrumb of your path. I was also thinking of doing a Kialo like UI element to show you where in the "tree" you are.
https://www.kialo.com/tour
I was also planning on calling the larger structure "tables" not "lists".
Since the table editor would also have to handle external JSON, I was also going to include the concept of "tabs", ie varients/algebraic data types.
I had initially written off links as a "database-like" feature of ie AirTable, but now I'm reconsidering that. They may be useful for raw data.
Do you think these would be improvement? Any further suggestions?