Could a cacheing service let static sites be cached when offline? I'm not sure if caching sub-domains like this would work but if its a tiny fee to cache maybe that could be a paid feature if your designing those. Like $1 per month could give you a static domain and XX monthly cache updates? As opposed to uploading somewhere like Github Codespaces or a Cloud-Flare service.

Direct real-time connections could be a path like nl.gg/# or a private key that someone could change. Some way to have a public site thats hosted globally for 'nearly free' while also being able to locally host a private url to the dev version for sharing temporarily while your connected. Maybe even a totally different domain.