The vast majority of headings (div/head) in the Guidelines use title case, but there is a minority that are in sentence case. I propose that we:
Make our minds up about which we should settle on.
Make all existing headings consistent with the decision.
Document it in the Guidelines style guide (http://www.tei-c.org/Activities/Council/Working/tcw24.xml), which has no mention of the issue.
The Journal specifies title case, but personally I prefer sentence case. Consistency is the most important thing, though.