In an email to this group on 18 February 2012 and on a page on this site, Leif Johansson proposed the notion of a formal IANA registry for Entity Categories. IANA registries must be defined in an IETF Internet-Draft that becomes the basis for a formal request to establish the registry. One of the clear advantages of such an approach is that the Internet-Draft includes process and governance proposals as well as information on syntax, semantics and other formal features of the proposed registry.
If the MACE-Cat group were to adopt and operate by as many of the provisions of such an Internet-Draft as possible, then even without (or prior to) formal IANA registration we would have public, well-defined processes and policies. The alternative would be to do the same definitional work, but not cast it as a proposed IANA registry.
Leif had previously submitted an Internet-Draft for an IANA registry for level of assurance profiles. As he notes, that document could serve as the starting point for a draft entity category registry proposal.