See my comment upthread, it helps a bit, but does not close this hole since apps within the same profile can communicate through IPC, so other apps could provide network access on their behalf. I think the best example is probably Play Services, which provides functionality for a lot of apps and will communicate with Google, etc.
(Yes, you can disable network access to Play Services, but it sometimes breaks things and the general point of IPC as a hole still stands.)
(Yes, you can disable network access to Play Services, but it sometimes breaks things and the general point of IPC as a hole still stands.)