Windows 8 Developer Preview is out (for x86/x64):
http://msdn.microsoft.com/en-us/windows/apps/br229516
I'm not sure if the included build of Visual Studio Express yet supports cross-compilation to ARM, but this will almost certainly be the case soon.
Thus, if Toni can eventually update WinUAE to support the Windows 8 SDK (retaining backwards compatibility with older Windows), and also allow builds which do not depend on x86-specific code (as with the experimental x64 build), cross-compiling an ARM build may not be too difficult.
Unfortunately, it appears ARM builds of Windows 8 will be "locked down", like the iPad, with apps only available through Microsoft's app store:
http://www.guardian.co.uk/technology...ft-tablet-apps
Presumably WinUAE will have to be downloaded from there on ARM platforms, rather than via the web.
A Windows 8 version of WinUAE may eventually benefit from a "Metro" touch-compatible interface, which is what MS are pushing now for ARM tablets.
But Windows 8 is still a year away from final release.