They make is so easy to login to the phone -- I'm still waiting for the ability to add multiple users. When I hand my phone to my daughter she should see her apps, my son, his. And when I hand my phone to my wife, she should unlock it and see.... her phone. If 256GB local storage and 11ac WiFi isn't enough storage and bandwidth to make this easy, I would be OK if it only kept the last GB of the camera roll.

Of course this sync should happen directly between our devices when they are on the same network. No need to go through the cloud.

By default if her phone rings it should only alert on her primary device. Unless she authenticates to my device at which point everything is there waiting. If her phone was ringing and she picks up my device and authenticates it should answer the call.

Ideally this is all smooth enough that we have matching devices and don't care which one either of us walks out of the house with.

The end game is that when networks are fast enough, the cloud mature enough, and homomorphic encryption performant, we get to the point where the phone basically lives in the cloud and anyone can pick up any iDevice, authenticate, and be looking at effectively their own device.