Interesting. You can set up the server to respond with 200.html as the catch-all so the requests would return 200. There was some issue with it—can't remember what—which is why I switched to 404.html. After the initial load though the subsequent navigations would go through pushState so I think they'd be cached.

But I don't see this is as big of a problem. With this I can switch and choose—SSR dynamic pages or use hacky catch-all mechanism. For any reasonably large site you probably would SSR for SEO and other purposes. But for completely offline apps I have to do zero extra work to render them as is.

Personally, I much prefer route paths vs query parameters not just because they look ugly but because they lose hierarchy. Also, you can't then just decide to SSR the pages individually as they're now permanently fixed to same path.