There is something wrong with your description that withdrawing bitcoin at a 6% per year rate would completely deplete the bitcoin in 16 years.
My underlying presumption is that any time that we are attempting to withdraw bitcoin in a sustainable way, then the withdrawal rate is sustainable in perpetuity, meaning that you can continue to withdraw at that same rate forever and ever and ever.
Sure, the size of your bitcoin stash will continue to go down, once you start to withdraw from it, yet its dollar value should be going up at a faster and larger rate than your withdrawals from it.
For example, I assert that right now, a person who wants to have an income of
$80k per year perpetually into the future and even with a 7% increase in the fiat withdrawal rate, can have 15.547 BTC and start immediately to withdraw at $6,667 per month. Of course, if a guy is worried about having enough of a value cushion and or making any mistakes, then he could have a little extra BTC, so maybe to get started the guy has an extra 0.6817794 BTC ($80,000/$117,340), so that he withdraws the first year in advance and still has 15.547 BTC, so then when next year comes, he will see that he still has enough to withdraw an additional $85.6k (which is $80k X 1.07 to account for a 7% increase in the cost of living or a 7% decrease in the value of the dollar).
Thanks for doing some explaining that brightened my knowledge. My calculations was based on mere expectations an ideal one. If the holders stops investing in bitcoin that is, if he doesn't add to his portfolio anymore, and assuming his withdrawal are on fixed bitcoin 6% with a reference value from the beginning of his withdrawal. Maybe that's where I got it all wrong, even without the 200WMA if the 6% withdrawal was to be continued it's value should be measured in USD and not in bitcoin and also at every new amount left in the portfolio the 6% conservative should be calculated from there. Well but thanks to you for giving me a clearer insight, now I get the whole picture of this sustainable withdrawal method rather than mistaking it for a depletion method to exhaust all your bitcoin in a limited amount of years.