The waterfall process for choosing the best canonical uri for a code system is good, *until *the last default is proposed:

"If a code system is not resolved by this list, and there is no publisher to consult, implementers must choose a URI to use. The priority should be to choose a unique value that won't accidentally be used by another implementer for a different purpose - or a very similar purpose with a different scope. "

A process that uses some official FHIR request process needs to be implemented so that a good and consistent strategy is used to generate needed code system URI when not available. This should be managed by Vocab WG or some other appropriate group and could potentially utilize a some sort of "URI generator" that takes input from the submitter to propose a URI that is consestent. Also this would need to establish a process by which external terminology authorities can be notified when HL7 is "making a URI" for their code system.