I'm not sure about this:

An "infinite" canvas without some notion of recursion such as viewports feels incomplete.

Check out charkoal.dev it has nested canvases and a few other extra features.

It is a great VSCode extension as-is, but the maintainers have abandoned it and they keep refusing to make it open-source. Someone is bound to make an open-source copy soon.

A file node can be a .canvas, so a .canvas can have nested canvases.

Obsidian's implementation of JSON Canvas supports this.