If you'll forgive me for my unsolicited advice, I have some thoughts about what I would change...
As is there is already the option to switch from "About" to "Local Storage", which presents me with a blank page at a new URL to start creating my own structs...
What if you use the URL as the key in localstorage, and store the document as a serialized string there? Then I can create new blank documents by visiting a yet-to-exist address. Then the dropdown menu could be used to switch between documents... oh, I guess we're just back to files and folders then xD
...so if the goal is to have one global document that I can zoom into and out of (arbitrarily nested structs), perhaps I could select any block and blow it up full screen, hiding all data outside of it, but allowing child-blocks to be added. You could implement these as folds so you only show the struct to x depth, or move down into the struct, following the rabbit hole as it were.
As the complexity multiplies, I expect eventually I'd want the ability to re-use blocks in multiple places, like a hard link, different paths to the same content. Then you get to visit a block in one place and ask "what are all the structs that include this block of text" ?
I always thought Wikipedia should work this way, there's so many articles on history and chemistry etc that have some context or background info -- very similar content produced by many authors. You should instead be able to embed a paragraph from an existing article and optionally pin it to a version/hash, but if its not pinned, you could update a hundred wiki articles at once by improving one sentence, and you could tell the computer, "show me all articles that embed or quote this paragraph", Now we're getting Xanadu-ey!