There seems to be two views to the ARM adventure. Looking forward, and Looking back.
Looking forward we will see any managed apps written today, should run on ARM unchanged including the XNA games. With the ARM product feature Jazelle should be ported to be the CLR accellerator, now that would be big plus and certainly along the lines of ARM's type of answers to problems.
Looking back at native x86 programs running on ARM is unlikely to be a in the box Microsoft product. Although the many DSP and GPU type products typically bundled in the SOC could make the x86 emulation/translation viable.