RE: Manually created, well organized sitemap.xml, using all of the optional tags, kept up to date nicely, and <lastmod> can quickly be edited. When numberous pages are updated at one time, 'Sections' that the eye could pick up quickly would make updates even quicker.

It's just an XML document, so I see no reason that 'sections' can't be 'highlighted' with:
<!--##########BLUE WIDGETS##########-->

On the other hand, it's never been asked of me before, so I don't want to pop off with an answer. However, I've never seen a commented sitemap.xml, and what I thought would be a simple search hasn't hasn't been helpful. It's all about what the SEs will digest nicely.

Something like:

<url>
<loc>http://www.example.com/directory/sub-directory/page.html</loc>
<lastmod>2009-07-24T13:25-05:00</lastmod>
<changefreq>monthly</changefreq>
<priority>1.0</priority>
</url>
<!--##########SECTION BREAK##########-->
<url>
<loc>http://www.example.com/directory/sub-directory/another-page.html</loc>
<lastmod>2009-04-09</lastmod>
<changefreq>yearly</changefreq>
<priority>0.2</priority>

</url>