without going into any other details: section 3 refers to section 5 and
calls it a "registry". whether a registry for payment schemes is or
isn't a good idea is a different matter, but as it is specified right
now, this is not a registry, but a fixed set of options. if you think
that a registry (that can be extended by adding new entries as the
payment space evolves) is a good idea, then you might want to consider
setting up an IANA registry a la RFC 5226 as part of your draft.