It seems one simple way of addressing this situation is to simply to revert to the IKEv1 wording, which would simply involve deleting the phrase "to pass an account name or" from the specification.
If we were to do this, which would make the use of ID_KEY_ID unambiguous, it raises the next question: should we create a new identity type that contains an account name, with some kind of tight specification about the use of UTF-8 or whatever.
--Paul Hoffman, Director --VPN Consortium