At some point in the curriculum of most schools and organizations, ranking ceases to be technical and becomes political. Typically in traditional gendai budo, the teaching curriculum extends as high as about 3rd or 4th dan. So, what should be the rank requirements for higher Dan grades - say, past about 4th dan?
Some general ideas of mine...
- Time in Grade - A pretty good rule of thumb for time in grade is it should take about as many years as the rank you are progressing toward. For instance, a shodan should stay shodan for about 2 years before they are ready for nidan. A 4th dan would stay 4th for about 5 years before being ready for 5th.
- Age minimums - Children, regardless of how long they have been practicing the skills, do not have the maturity to be black belt. Children should not begin in a regular adult class until they are about teenage, and they should not achieve shodan before about age 16-17 (and possibly not even then).
- Shodan (1st degree black belt) traditionally does not mean "master" or even "teacher", but rather more like a "beginner that has taken the first step." A shodan is someone who can safely and competently practice a large portion of the superficial teaching syllabus, and is ready to delve deeper into the art.
- The Nidan (2nd black belt) is still working on the fundamentals but is beginning to diverge a bit from his teacher - or at least is beginning to see where the art may have to be modified to become his own art.
- Through about 3rd Dan is generally considered student ranks. Achieving 3rd dan means that you have seen and practiced the whole teaching syllabus. In the case of judo, for example, a 3rd dan should know the entire gokyo, katamenokata, and nagenokata.
- Yondan (4th black belt) begins the actual teaching ranks, however, in The United States, there are often not enough yondans to go around, so lower-ranked practitioners are often called upon to teach - especially in local or grassroots clubs. Often these 2nd and 3rd degree black belt students are actually the best teachers in the system because they still remember what it was like to be a beginner and they are still diligent about teaching the syllabus unchanged. Also, if a student is expected to assume the role of teacher by yondan, then she had better have pretty extensive practice at it prior to that time. Therefore, students should be getting progressively more teaching responsibilities starting at about brown belt, and sandans may have been teaching long enough to have shodan students.
- Godan (5th degree black belts) should have been teaching long enough to have produced at least one student of sandan level. One might wish to to extend that scheme to higher ranks, such that a 7th dan should have at least one 5th dan student and a 9th dan should have at least one 7th dan student, etc...
- Regarding terminal rank - the idea that except for truly exceptional cases, most people should max out at 3rd to 5th dan - I think that in order to advance you should be physically able to do the skills appropriate to that level - so you probably shouldn't be able to achieve 9th dan just by surviving long enough if you are incapacitated by health problems or physical conditions.
- Shiai for rank - In many clubs (historically - but not so much anymore), you are expected to compete to advance. That might mean you go to tournaments to collect points toward a promotion requirement, or it might mean an in-club shiai where you compete against your classmates to gague your preparedness for rank. I think this is 100% appropriate for student ranks in kids and young adults, but it is ludicrous to think that a 70 year-old 7th dan ought to compete against a bunch of young adults in order to become 8th dan. I do think that kata competition or demonstration could still be appropriate.
So, basically, most of that verbiage lies around the idea that technical requirements and tests apply up to about 3rd or 4th dan, and advancement beyond that should mostly be based on time, service, and teaching.
How do you quantify and "test" for time, service, and teaching beyond the above bullet points? I don't know.