Earlier quoted context omitted.
The intention is to make use of the new "Origin privet file system" api, this provides the website with a sandboxed block level file system on the users device that can be used for efficient access and writes. It will be possible for WASM SQLite, or any other DB engine ported to WASM, to have full ACID compliance. The SQLite team have been working with browser developers to ensure the new API is sufficient to enable…
Unfortunately unlike apps, the system doesn’t support backing up local storage managed by the browser, so if you get a new phone, you lose your data.
I think the idea is to still sync to a server, but support offline (and low latency!) use too.
It's "offline first", not "offline only".