[mikeash]

I find it odd that your first comment is a complaint that setting up a new user actually acts like a new user. Of course your settings didn't carry over. That's the whole point of separate user accounts.

I see no need to overcomplicate it. A user account system where each account acts like a separate device (aside from the unfortunate realities of sharing storage resources) would be fine. What apps share state? None! What music gets shared? None! What settings get shared? None!

[Too]

On fixed hardware devices things are a bit easier, but consider a desktop PC with Windows. If i install a driver for my new printer, should user B also have to install that driver? Should every family member have to install a printer driver?! To make things even worse replace printer with something necessary to even run the system properly like graphics card driver. Another food for thought is windows update. I consider the keyboard localization in android to be of similar system-wide-configuration kind and shouldn't have to be redone for every user, someone else might not. (As a side note changing to a localized keyboard in android is in fact much harder than installing a driver in windows).

When does something cross the line from "system wide driver/configuration" to "user specific data/configuration"? If absolutely everything should act like a separate device you might as well dual boot or use virtual machines.

One of my scenarios for shared data is that when I'm working i want to listen to my music, but when i have a party i want to use the same device as a jukebox with the same music but not open up access to my documents. I know that i'm not alone with this problem. Trusting your friends to not dig around is another topic but with pop up notifications and active widgets on the desktop even your most trusted friends might get private emails shoved in their face even if they are trying to avoid them.

[mikeash]

OK, but we're not actually talking about desktop PCs, but iOS devices. There are no drivers to install. There are almost no device-wide settings at all. Exceptions would be OS updates and stuff like Find My iPhone. Easy solution there: allow one and only one "owner" account to touch them.

The idea that keyboard localization should be system-wide is weird. Different people can speak and write different languages. Although it should be a non-issue, since a single person can speak and write multiple languages, and switching keyboards should be trivial.

Anyway, you can come up with scenarios where my "make it act like a fresh device" idea is inadequate. But my idea is still an absolute improvement over what we have now, and would be perfectly good for a lot of uses. You're describing a bunch of stuff you want but that is by no means required, and then using the complexity of that stuff to say that the whole feature is a bad idea. It doesn't make a lot of sense.