Emulation is NOT the answer
Cross instruction set architecture emulation has been tried many times over the years with mediocre results. Even with hardware 10x faster than the emulated ISA, the performance has always been abysmal. Also ARM and x86 couldn't be more different. The x86 ISA is exceedingly complex whereas ARM is a minimalist RISC architecture.
Microsoft is opting for the more tractable approach of recompilation. Since very few apps are done in assembly these days, this is a quite feasible, good performance approach. MS will be putting a lot into Visual Studio to make this process as painless as possible..
My understanding is that at RTM running legacy apps will have about the same experience as they do now on W7. There will probably be some tweaks to let a mouse substitute for your finger when using desktop monitors.
