This looks really cool! I’m interested to see how this develops, as there are a couple of features that I would probably need to see before switching over to something like this.
Variables in page URLs: I’m not sure how this would work in this setup as it adds significant complexity, but I have pages based on locations like /foo/{id}/bar, where callbacks that lay out the new page rely on the {id} from the URL.
Keeping state in URL params: again, probably not relevant for the use cases you would imagine here, but I’ve previously hacked together (admittedly horrible) solutions for having layout properties stored as parameters. Easy for a single page, but cumbersome for multiple pages.
I’ll be looking at implementing both of these properly in the coming months, so I’ll be looking for inspiration from features like this.