The only reason I stepped into this discussion was to clarify whether or
not the OPTIONAL use of RC2 is a violation of IETF guidelines, and as
far as I can tell it isn't.
At least for the case of MIME content-type names, we allow assignment
of names for proprietary content-types. This was simply pragmatic:
there were (unfortunately!) too many proprietary content-types that
people wanted to use in MIME, (and were going to be used no matter what
the IETF said) and we're better off having them clearly labeled.
I imagine that the working group will want to use some kind of
algorithm identifier to specify what kind of encryption is being used.
If so, the working group could decide the rules governing assignment
of algorithm identifiers, and (for example) whether the algorithm had
to have a published and openly available specification. My guess
is that a set of workable rules would end up being much like those
for MIME types.
Keith