It sounds like we need to decide whether non-PKI aware, non-ASN.1-capable clients need to be supported. If so, we should probably define a set of requirements for such clients and include this item in that list. I would suggest that such clients are an important group and should be supported.
I put this question to the list in my strawman spec over 2 weeks ago, and have not yet gotten a concrete proposal on how to accommodate such clients. I will soon decide that we will NOT support them for now, unless I see such a proposal.
--Paul Hoffman, Director --Internet Mail Consortium