I know this is a Unity thread, but Windows 8 support was brought up here (and in the feature request section) a couple times. As someone with a game up on the Windows 8 store that was featured around launch, (also had a launch title with Windows Phone 7), my opinion is that it’s really not something you have to worry about right now.
My game (Geared) is available on iOS, Android, Windows Phone 7 (as Revolution), and Windows 8, and the windows store performance I’ve seen isn’t even close. The concept of the app store is a new feature to the Windows desktop platform, and it’s going to be a while before the Windows 8 Store really delivers sizable revenue for developers.
For Geared.
iOS and Android - Over a million dollars in revenue.
Windows 7 Phone - $27,000 (Launch title, Managed Game, featured by Microsoft)
Windows 8 - $5,100 (Launch title, featured by Microsoft)