I’ve not had time (nor the will) to install the Windows 8 Consumer Preview yet, but those who have say the metro style works very well. Since the public at large finally has access to the Metro UI, it makes sense for Microsoft to release an SDK for Bing Maps.

Licensing has been changed to take advantage of Windows 8 Preview:

Along with the new controls, today we’re also announcing a new licensing model for the pre-release versions of Windows 8, providing you much more flexibility in developing and testing your Metro style apps on the Consumer Preview. The new Terms of Use for Pre-Release Windows 8 Metro style apps allows free and unlimited use of Bing Maps controls and APIs within your Metro style apps for the duration of the Windows 8 pre-release period. Additionally, you are encouraged to submit your apps to the Windows Store for others to use during the preview.

That should make developing much easier so you can jump right in. I suspect Esri will jump in on this Metro stuff quickly as well.