long time ago I proposed that the ultimate safe withdrawal rate is to liquidate no more than the amount the value of the shares has increased. Prices might go up and down, but the real value of your holding would never change. You could withdraw money forever, or at least as long as the real value kept rising. Since valuation metrics are themselves pretty volatile, I proposed using a smoothing method.
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Just for clarity the amount liquidated to preserve value is of course be the amount the quote (ie. the nominal value) has gone up, minus inflation.

Just to clarify, no, that isn't at all what I proposed. I proposed a system wherein the number of shares you sell is such that the real VALUE of your total holding is unchanged, not a function in any way of the current quote (nominal or real).

The method you propose is not so different, but only in the instance that the real growth rate in value per share remains fairly constant. It will cause you to erode the value of your holding very substantially if the looking-backwards rate of value growth is higher than the current or near future rate. Had you started that early in the century, you'd have been in trouble pretty quickly. Assuming I understand your proposal correctly, I estimate that the real value of your shareholding would have been down by half in 5 years. Value was rising on trend at around inflation+8%, but the estimates would have started around 21% falling to about 16%.

The method I proposed adjusts to recent rates of value growth within about a year and a half so there isn't very much danger of overestimating the current value or overestimating how much can be sold without eating into the capital. The risk exists, but not for long. The smoothed value line bends to a new slope within a reasonable amount of time, reacting to recent business results. The goal was to have something that reacts quickly enough to avoid extrapolating old high rates of value growth, while being just slow enough that a dip in the value metric during a recession doesn't cause the value estimate to cease rising.

Unless we see a long stretch of truly terrible business results, of course: nothing will save a fancy strategy if the underlying security no longer rises in value!

Jim