Every estimate of an upper price for #bitcoin must be time bound or it makes no sense. The supply isn't 21 million, many coins are already lost. People will continue to lose coins forever. The supply had a theoretical max of 21 million. The supply will never stop changing, it will just stop growing and start shrinking.

That means fractional sats will one day have to be a thing. If bitcoin lasts long enough a fraction of a sat may one day be more valuable than a whole coin today.