Android VPNs are per-user. A user here can mean either a user you create from Settings -> System, or a work profile. All can have their own individual VPN.
If you have a VPN running, and then create a new user or work profile, the VPN wouldn't apply to those users.
This feature could make it so that it optionally applies to them too.
It's basically part 1 of #349
To further extend this, we can have one VPN that's useful across
- The entire OS, all users
- Current "user" and all of it's work profiles
- Any other combination, should all be doable via uid ranges.