allowing appendices to be grouped

We have some customers who want to be able to group
their appendices in their bookmap and have a topichead
that shows up in the ToC for the group of appendices.

This would parallel the way one can group chapters
in a part.

In fact, the first suggestion was to allow appendix
in part.  This would be an acceptable solution for
our customers.

Another solution is to add a specialization of topicref 
called "appendices" (or whatever) and change the content 
of bookmap to be:

<!ENTITY % bookmap.content
                       "(((%title;) | 
                          (%booktitle;))?,
                         (%bookmeta;)?, 
                         (%frontmatter;)?,
                         (%chapter;)*, 
                         (%part;)*, 
                         ((%appendices;)? | (%appendix;)*),
                         (%backmatter;)?,
                         (%reltable;)*)"
>

where appendices has a content model of (%appendix;)*.

Can the DITA TC consider this issue and see if either or
both of these solutions is something we can do to bookmap?

paul