Possible Architectural issue with XHTML modularization?

I just looked at the XHTML modularization rec, and it doesn't
seem to say much about namespaces, except that if you put in
new stuff, it has to be in a non-XHTML namespace - perfectly
sensible.  But the top-level namespace is still that of XHTML
I gather?  Modularization is signaled using the public 
identifier in the DOCTYPE declaration; see section 3.6 of

http://www.w3.org/TR/xhtml-modularization/conformance.html

I'm not sure what I think, but it does feel relevant to
our recent discussions. -Tim