It is an interesting idea... something along the lines of the sounds database that NI and others have implemented in their software synthesizers I imagine?
But there is a catch... one can tag files, but I do not know if Windows supports tagging directories. So that leaves us with a couple of options, neither of which would be terribly difficult to implement... and a Sonar project consists of a project file (or many versions of the project file) and all the audio files, and in some cases some of us store presets for synths and effects in that same folder. It gets ugly pretty quickly!
IF windows supports something like ID3 tags for folders then tagging could be done at the project level (or so it would appear to the user) and at the folder level (as it appears to the OS), and explorer already provides the means to search and sort based on tags.
If windows does not support ID3 tags for folders then we'd need Cakewalk to provide a chunk in the project file format that supported ID3 tags. Then we would need an additional tool to transparently search the Cakewalk Projects folder for project files, and display the meta-data for those files. But that's really just an extension to windows explorer, and that is pretty well documented and supported.
(I built a quick PERL script to list all my projects by date, size or name, and it worked pretty well for a hack.)
None of the above would interfere with the way that most of us store projects.
Quick note to those that are curious - wave files support ID3 tagging. I forget what I needed to do to make it work, I think it was simply defaulting to broadcast wave files. It's handy - I can tag everything using any ID3 tagging tool!