Versioned Public IDs: why only shells?

I'd like to know if this is deliberate,
or an oversight, or Not The TC's Problem.

So we have versioned public IDs for
DTD shells now:

  "-//OASIS//DTD DITA 1.1
Concept//EN"

Good, that helps interoperability when
not everyone has upgraded to DITA 1.1.

But I don't see versioned public IDs
for the elements/entities files:

  "-//OASIS//ELEMENTS DITA
Concept//EN"

but not

  "-//OASIS//ELEMENTS DITA
1.1 Concept//EN"

Why?  Are the contents of the modules
guaranteed not to change, ever?  It seems that they already have changed
from 1.0 to 1.1.

I can imagine situations where I will
be using both a DITA 1.0 Concept shell, and a DITA 1.1 Concept shell, at
different times.  Each shell DTD contains the lines:

<!ENTITY % concept-typemod

           
            PUBLIC

"-//OASIS//ELEMENTS DITA Concept//EN"

"concept.mod"    
                     
                     
       >

%concept-typemod;

By not having a versioned public ID
for "-//OASIS//ELEMENTS DITA Concept//EN", I can't select a 1.0
concept.mod vs. a 1.1 concept.mod except by having no catalog entry for
"-//OASIS//ELEMENTS DITA Concept//EN", allowing the public ID
lookup to fail and to fall back to the system ID, which I can arrange to
be in separate directories.  But then I have to have a concept.mod
in every directory that has a shell DTD, including my own company-specific
stuff.

-- 

Deborah Pickett

Information Architect, Moldflow Corporation, Melbourne