Windows 8 "Blue": Cloud-enabled experiences
As a developer my number one item on my Windows 8 "Blue" wishlist is for Microsoft to open up the Skydrive platform to enable Cloud-enabled experiences.
The backbone is already there. Every single user of Windows 8/RT/Phone 8 already has a Skydrive that you can back up user data to. Imagine if that same Skydrive, which is linked to the user, also backs up application data, which can be hooked into by application developers.
Here is a first-party example using Xbox Video. A user Rents/Buys a movie on their home desktop/laptop and watches a portion of it. When they finish watching the Xbox Video app uses the Skydrive back-end to sync their current location in the movie. The next morning on the train to work the user uses their Surface to resume the movie at the exact spot they left out on. During work they sneak off to the bathroom to watch some more while they take a dump, again, resuming at the exact spot they left off on when they exited the train.
All of this enabled by a Skydrive API that app developers can take advantage of.
That is my vision of Windows 8 "Blue".