I've added support for generating Windows Runtime assemblies with IKVM.Reflection. This is still experimental because it is mostly based on reverse engineering as there currently is virtually no documentation on this.
The code for generating a trivial component is available here. It doesn't require .NET 4.5 or any Windows Runtime metadata assemblies.
The IKVM.Reflection code is available in cvs.
BTW, I did this mostly because I was curious about what's involved. Don't read anything into this wrt IKVM.NET itself. It's unlikely to ever support running in WinRT.