I guess some of my response comes from my medical background, as well. You've got a M.D., great, congratulations. You still get to take further tests to get licensed to practice medicine. After you get that license, you still have to maintain a certain standard of practice and continuing education to maintain your license to practice in an ongoing fashion.
That's just it. Medicine is a profession with real standards involving a vital service. It's in the public eye and has objective standards for accreditation. The accreditation process for schools is standard as is board certification. Since human bodies and the technologies to diagnose and treat them are pretty much the same everywhere it's straightforward to do this. Also, real human lives are at stake all the time. Patient comfort is important, but getting certain real-world results is the real issue.
Martial arts is nothing of the sort. The MA world is largely built around brand loyalty and personal loyalty. It's the image and mystique as much as anything else. That leads to cults of personality and the elevation of personal issues to core concerns. Under such conditions it is almost inevitable that likes and dislikes and the power to grant or deny status will be important. That means, of course, the power to take them away.
The AMA can vote in new directors. A State Board of Regents can replace medical school faculty. Congress has gotten involved when the process had to be corrected. There are sources of correction and feedback and ways of keeping the profession on an even keel. This is not the case in a martial arts association. And I'm not sure how it could be unless we went the government certification route or most students suddenly had to make the training work in life or death situations all the time.
What is a black belt after all? It's a license to teach, but it's also about status, hopes and dreams. Combine the two, and personalities will rule as often as not.
Will you ever be stripped of your M.D.? Probably never.
Will you ever be stopped from legally practicing medicine? You bet, if your skills and knowledge are not kept up to snuff.
Would you be eligible for further training (e.g. fellowships)? Probably, although you must demonstrate that your skills and knowledge provide a sufficient basis for further specialty training.
Think of it this way. Suppose you got a degree fifty years ago. No matter how reprehensible you were later or if you never cracked a textbook again you would still be Joe Blow MSc. You might not be current on the state of the field, but there's no denying that you earned the degree and can put it on your resume. What goes on in the martial arts world is more like saying "You know that diploma we gave you? We don't like you anymore, so we're taking it back," or "You have to pay us a fee every year or it goes away."
I stated that I did not believe that such a drop off meritted stripping rank or requirement of re-certification. I did state that if a black belt did not keep skills current, then they could rightfully be required to remediate prior to further rank progression.
That's very reasonable. Some martial arts work that way. To become a Godan in Judo you have to pass certain tests and win a certain number of tournament bouts. If you can't, you have to wait until you can. In Kendo the hachidans really are good enough to beat pretty much everyone at the levels below them. A BJJ black belt has to be better than the brown belts and hold his own rolling with the black belts. After that the number of stripes really doesn't matter. That's part of the standard.
In the case of the 80 year old 7th dan or the 40 year old 1st dan with emphysema, no, I would not expect them to be stripped of rank. Also, I would not expect them to be eligible from further ranks, unless they could meet the standards of the next rank.
There's something else at work here. In most martial arts, after a certain point ranks are honorary. There's a certain degree of rank which comes from passing tests and being able to win fights with people. Past that they're understood to be for less concrete but theoretically important contributions to the style. The difference between eighth, ninth and tenth dan in Judo is a matter of perception and institutional regard. The Ancient and Venerable Fossils with the really fancy sashes are all at a certain minimum level. The extra flourishes and funny hats are just icing on the already-baked cake.