The discussion seems to imply a need for new HTML markup to accomodate
this functionality. I believe that the necessary new functionality is
being proposed for HTML (but some preprocessor for producing the
appropriate HTML may be also be needed?). The two existing proposals
that I believe provide the required HTML tools involve the attribute
CLASS and the element FN.
I believe that the CLASS attribute proposed as part of the style sheet
discussion, especially the ability to collect/specify multiple classes,
can provide the identification of change submissions and/or
contributor. CLASS can also be used to identify the types of changes
mentioned (new, deleted, moved) and an appropriate style sheet can
render them in a manner in which each can be distinguished.
e.g. <SPAN CLASS="fred added">new text from Fred</SPAN>
The discussion about "meta-text" (e.g. comments/justification?) might
be handled with the proposed footnote <FN> element. Footnotes, coupled
with identification of various CLASSes of footnotes (comment, or
justification, or alternative text), might provide this functionality.
At least I can see a way to do this with these tools. Does this seem
to be adequate for the functionality you have explored?