it would be nice if the page would also highlight the id/class block structures.
I recommend the Firefox web dev tool kit for that.
I like the static XHTML idea. I prefer it to the module (as I think this will just end up having the same problems as trying to theme a live site - that is, we cannot guarantee all dynamic content is appearing at any one time).
I like the POT analogy. Can we create a script that will distill out the XHMTL from modules? Perhaps running bits and pieces of drupal to capture the output. Since all HTML should be in theme_* functions, this might be easier than it sounds....
-Mark