Here's something vaguely related in State of the Onion --

Larry mentioned that overloading was a headache; you hate it in languages that have it, and you hate it when languages don't have it. Sometimes there are gratuitous abuses of overloading, such as C++'s left-shift operator to add more arguments to a function. The overloading system will be a lot cleaner, by specifying operators as special method names. The vtable system will be leveraged to provide overloading on objects. There will also be overloading hooks in printf so that new formats can be defined.

he's probably open to the idea of custom (un)pack formats if he plans on custom printf formats, if the two aren't part & parcel.