Since it sounded like jQuery was an option for Metro JavaScript apps, I was starting to look forward to Windows 8 dev. I installed Visual Studio 2012 Express RC and started
If you still need it, I am writting a reimplementation of the Deferred object found in jQuery.
Once finished it should be 100% compatible with jQuery's Deferred object. Right now it's quite complete but needs some testing.
See this.
Hope this will help!
That said, I think it should be a good idea to learn how to use Microsoft's implementation of Promise instead of jQuery when working on Windows 8 apps.