DITA 1.2 suggestion--Inserting a ditamap into a bookmap

This is a DITA 1.2 suggestion to improve how one inserts
a ditamap reference into a bookmap.

The problem is that, to reference a ditamap from a bookmap,
one might have a bookmap that looks like this:

However, this can be very misleading since the things in
the referenced ditamap file may or may not be chapters.
Having to use chapter to reference a ditamap from a
bookmap is therefore very confusing to users.

We could allow topicref in bookmap's everywhere chapter and
part are currently allowed.  That would permit:

However, allowing topicref would open to door to references
to other things besides ditamaps.

The preferred solution would be to create something like "mapref"
as a specialization of topicref with a fixed value for format
of "ditamap" and possibly a fixed value for scope of "local".
(I'm less sure about scope, but I can't think of a case where it
makes sense to have a topicref to a DITA map that isn't available
at the time of composition.)  That would allow users to enter:

which would be a lot less confusing than the current situation.