sorry microsoft, you had this already
I remember the days of Windows CE and windows mobile 6 devices. That's the closest they ever got. While those devices had very little connectivity, couldn't store much data, and had annoying restrictions on programs, they had a basis that could lead to what would be useful. At that point, you synced all your data over a cable, so that was annoying, but the theory was there: keep the same documents, e-mails, calendars, etc. on each device and make the programs to use them similar enough that you don't have to learn two, but not so similar that the interface for one of them is terrible. If they kept up with that theory, eventually uniting the two operating systems enough, they would have what people want if they want the two devices to be essentially the same. And people bought those devices, so they had an existing user base.
The hardware of today and of five years ago would be perfect for this. Extra storage would allow for keeping all the documents stored, at least for most people, on the mobile as well as the desktop or laptop. WiFi and bluetooth would ensure sync was fast and occurred in the background, so things wouldn't be missing from one. That'd also lead to a ton of cloud customers for a your data is completely backed up a la dropbox solution. It would have ensured customers for microsoft, as its control over the desktop and office areas would have helped to drive the sale of "completely connected" mobile devices.
They had the basis they could build on. So what did they do with it? They wrote windows phone 8. Well, I give up.
Biting the hand that feeds IT
