GNOME Single Sign In
Ostensibly a free software/service single-sign-in equivalent to Apple ID/Microsoft Account/etc. where a compatible and optional cloud service would allow you to "Sign into GNOME" wherein things like app settings, personalization, install history, keyring, etc. would be synced.
Design-wise this is how it integrates with the desktop--I'm thinking in Settings > Users, somehow where the cloud account is tied to a local account--and how the experience changes if you're signed into such a service.