You could of course disable network access to Play Services, but at least for me that broke a bunch of apps or made them unreliable.
What AOSP ROMs need besides the network permission toggle is IPC scopes functionality, akin to storage scopes.
If you want something less disruptive for isolation, there's Private Space. What I like is that this can stop apps there from working in the background on stock Android as well.
Folks brings up 'IPC' as if this is some chink in the armour in AOSP. It isn't. 'Apps' pretty much on most consumer OSes can 'IPC' their way with other co-operating apps to 'achieve' network access from behind a firewall, just the same.
> since many apps communicate with Play Services and as far as I understand (but I may be mistaken) Play Services does work that involves internet access on behalf of other apps
If the OS or its privileged component will fchown the socket to the origin app, think the INTERNET permission will be enforced as expected.
I am not familiar with iOS internals, but does "very little IPC" mean "zero IPC"? Because if we are talking IPC in the context of bypassing permission checks, I imagine, 'very little' doesn't cut it?