Extended conforming packages and manifest:algorithm-name

We recently discussed removing the "extended" conformance clause for 
packages.  This was in :  
http://tools.oasis-open.org/issues/browse/OFFICE-2257

I think the idea was it was only used when there were additional files in 
the document beyond those defined by ODF.

However, I found another place where "extended" conformance is triggered. 
Part 3, Section 3.8.1 defines the allowed values of the 
manifest:algorithm-name attribute, and says:

"The IRI of an alternative algorithm as specified in §5.1 of 
[xmlenc-core]. Alternative algorithms may be specified by extended 
conforming documents only. They shall not be specified by conforming 
documents."

So if we eliminate the extended package distinction, then we allow 
conforming documents to be encrypted using proprietary algorithms, which I 
think goes against the interoperability benefits we were trying to foster 
by making the extended/non-extended distinction.

I don't think I'm in favor of this change.

Anyone want to argue otherwise?

-Rob