This question might be slightly more appropriate on the [hidden email] mailing list, where discussion of kerberos-related standards work occurs.
(I don't really expect it to be more likely to receive a useful response
there than here, though.)
I don't know of any additional work on it; such protocol extensions cannot
reasonably be deployed without going through the IETF process, and there
would be a record of actions occurring within the IETF (such as on the
archives of the aforementioned mailing list).