Andrew, You do a great job here thanks. You make it really easy to understand, when the problem is straight forward with two Apple IDs. But there was periodes in time, where Apple was making adverdises about having 5 and later 10 devices in your family - never mentioned here. There were @mac adresses, then my own mailadresses, then the famous Family account, payed for years, and did stop this may. Then iPad and FaceTime did show up and they like to have a unique @me adress each. iPhone each, AppleTV and MacMini Server....
Out of this chaotic number of Mailadresses and Apple IDs and Cloud ID to syncronize the families calendar and addresses and... and several Apple IDs for App Store and others for iTunes. The last iOS update for all our iphones - it was a totally nightmare. I instinctly choose the same password for all of the IDs to make it a little more easy. logging off and on and downloading and log off and on on all devices.... And giving every single iChat, iMessage and FaceTime on every iPad and MacBook Pro and iMac its own Apple ID, updating with 10 different Apple IDs in AppStore and iTunes is not as easy, as you descripe it Andrew.
When several people in a family are home on different times and downloading music on a Apple IDs they remember this day (but shouldn't), over years things getting real messy and complicated. A clean up in the Apple family will be a enormous help.
We can of corse have focus on, there may be some bad guys out there, using perhaps the opportunity to do any harm. Perhaps. Perhaps not. Should Apple punish the millions of Apple users forever, because of some "perhaps bandits"? Sometimes we create this Bandits in our head, writing about how dangerous this bandits in our head can be and then somebody get the idea and is willing to take the role as the Bandit...
Sometimes it is wise to use a good sword and cut the head of the snake, not waiting until the snake takes over and fear is stearing our life. You mentioned also how expencive it could be for Apple. It will not get cheaper by waiting.
Windows had a huge disadvantage - Microsoft trailed in all this years the original DOS, in every Windows update.
This was perhaps the major reason for a weak and unstaple system.
Apple has the Apple ID - a growing problem when not new and better ways are developed - solving this for single persons and families. Primitive solutions like 'one person - one Apple ID' will make it easy for Apple for a short periode of time, but is unbareable and enormous frustrating for us, who are creating Apples billion $ profits every year.
As a IT Engineer I was witness of the development since 1972 and did choose Apple because of the Visions of Steve Jobs, to create a better computer and create a better world. Not a awkward solution for a awkward world....
To find a way out of this mess and getting a little more clearness and understanding, this site was a huge help:
http://gigaom.com/apple/how-many-apple-ids-should-your-family-have/
Perhaps it makes sense Andrew