The TEI Guidelines (P5 edition) contain two chapters about character encoding issues, specifically revised to address the use of Unicode.
You can read the current drafts at http://www.tei-c.org/Activities/CE/FASC-ch.pdf (overview of character encoding issues) and http://www.tei-c.org/Activities/CE/FASC-wd.pdf (recommendations for encoding non-Unicode characters and glyphs
Comments on these preliminary drafts from the digiterati on this list would be particularly welcome.
Also, if you have specific proposals for changes or additions to the proposals, please visit http://tei.sourceforge.net and make a "feature request"!
Lou Burnard