But surely most of the coins were lost when they were cheap rather than now? If that's the case most of the deflation stemming from lost coins already happened and isn't going to happen in the future, so it's not really a big issue.
Unless they were only presumed lost. Imagine someone had the power to suddenly activate whatever fraction of the contemporary USD supply their family had in 1800, proportionally scaled to the amount of USD circulating now. And in the deflatory bitcoin world, the amount of tokens in circulation might eventually end up being merely a tiny fraction of what some presumably dead addresses hold. An address like that lightning up would be as if the Fed suddenly announced that they just issued a multitude of the USD previously in circulation. Not to banks, as credit, but to some guy (unnamed). "Nice currency you have there, world economy, I have the other half of it. Let's be friends shall we?"
Of course these are more hypothetical end game states than immediate threats (I think, I have no idea what fraction could currently be considered dark), but we can't just ignore theoreticals like that.
Would they even be able to cash out though? Even a small transfer from a presumed-dead wallet can trigger a massive market crash in your scenario. Now if they just want to watch the world burn, that’s another matter.
