Today Microsoft detailed their Windows On ARM strategy. At last, Microsoft has confirmed that Windows On ARM will not support any type of virtualization or emulation approach, and will not enable existing x86/64 applications to be ported or run. So, this leaves developers with the only choice. If they want to target both Windows On ARM & Windows 8 on x86/x64, WinRT API’s are the only way to go. Also Windows On ARM will allow you to install apps only from Windows Store signed by Microsoft.
Here is the reason Microsoft tell us,
Supporting various forms of emulation runs counter to the goal of delivering a product that takes a modern approach to system reliability and predictability—by definition, existing code has not been optimized for the platform the way WOA has. Virtualized or emulated software will consume system resources, including battery life and CPU, at unacceptable levels. Emulation and virtualization of existing x86/64 software also require the traditional PC environment of mouse and keyboard, which is not a good assumption for WOA PCs.
If we enabled the broad porting of existing code we would fail to deliver on our commitment to longer battery life, predictable performance, and especially a reliable experience over time. The conventions used by today’s Windows apps do not necessarily provide this, whether it is background processes, polling loops, timers, system hooks, startup programs, registry changes, kernel mode code, admin rights, unsigned drivers, add-ins, or a host of other common techniques.
Read more at Building Windows 8 Blog.