r.willis is confused about the BIP process.
It is not "Write a specification. Submit a BIP. Argue for a while, revise the specification. Finalize BIP, then everybody agrees to implement it."
I know there are standardization processes that try to work that way, and they're generally miserable failures. You end up with bloated specifications and implementations that don't work with each other because everybody interprets the spec slightly differently.
I like the IETF model, of working code and rough consensus. So, once the payment protocol is implemented and early adopters have had a chance to play with it, it will become a formal BIP. Until then, as Mike said, I'll be tweaking https://gist.github.com/gavinandresen/4120476 as I run into issues.