It's not killed IMHO, I actively use a fleet of such single HTML file apps that I save locally and even share with people. My initial comment has an example of a gallery, works wonderfully.
Well my issue is you forget to hit Ctrl-S/Cmd-S and your changes are gone. I've been using computers since early 90s and haven't found one program that does that; heck many apps don't even have an explicit "save" button, saving (and syncing) is transparent.
The web "browser" wasn't "intended" for this use case, hence the issue. This could be easily fixed though -- just like cookies.
You can also use localstorage/indexeddb and keep syncing it with a script element of type text/json. On-load, see if localstorage is gone (different browser, domain, etc.) and restore from the script element if that's the case.
I explicitly do not want such a thing in many of my HTML-apps, but one could add it with relative ease.
