File this under 'stuff we may not see for a long, long time, if ever'. In case you have not noticed, Microsoft has lots of "projects" that they work on that have 5 and 10 year outlooks on them. A lot go nowhere, others get folded into different programs and some are just for research-exploration in computing.
The latest one, via ZDNet is a Microsoft project called 'Menlo', which is headed by Galen Hunt, a fellow who also started MS's 'Singularity' project (which if you haven't read about, you should as it deals with a potential future OS rewrite).
'Menlo' is reportedly an attempt to replace the current WinCE core of Windows Phone/Mobile/Zune with NT, the same core that Windows desktop is built around. However, two sources from Mary Jo (one anonymous, the other an analyst on Microsoft), are doubtful of the idea, noting that WinCE is not really a problem and and that MS is pushing developers into using Silverlight, not WinCE for writing programs.
Still, like a lot of research programs, 'Menlo' could just be an exploration of the feasibility of developing a more powerful and ubiquitous NT core for mobile than an actual 'go ahead' to do so. Mary Jo hints at how having a NT core would allow developers to easily port software from the huge Windows desktop world to the mobile one (phone and tablets) with very little effort--similar to the current XBox/Phone push with WP7.
Finally, like all things dealing with these MS projects, you may not hear about this again for years if ever. But it is fun to get a glimpse into Microsoft's thinking about "...the future of computing when mobiles becomes users primary PCs". A future which is certainly coming fast.