1.1m is indeed a huge amount that would certainly affect the price be it done at once or in stages, however, the total daily volume of BTC trades is half a million BTC (today's volume), double the volume in the order book would certainly crash BTC price at least temporary.
However, the greater effect would be the fact that Satoshi's coins are moving, which would cause a massive drop in price for various reasons that the market would speculate.
1- Some people would think Satoshi lost faith in BTC and it's over.
2- Someone managed to "hack" into Satoshis wallet or brute-forced the seed.
3- Satoshi's identity is exposed and some x government arrested him.
Those along with other things that come from a lack of understanding of how Bitcoin and its security work, like Satoshi giving away the "key" to Bitcoin and thus it would be destroyed (many people think there is a source code of some sort that only Satoshi has, like a private server or whatever that would bring BTC down"
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Mostly it's all these negative speculations that would cause a massive drop price, which would then be recovered over time in my opinion.
Isn't there this warning application on Twitter/X that when dormant big wallets move their coins, there is an automatic message going out?
Assuming someone would successfully brute-force the seed, what value would it give to the person to move the coins first? I think they would set up an agenda, claiming that Satoshi is back. It seems as if that were not make a huge difference, but I think it would be much smarter to "reappear" on Bitcointalk and Reddit and so on and so forth, claiming to be Satoshi. Then giving it some time, write up a story, claim that anonymity is important so it is not possible for them to show their face. If they then began moving small amounts, I believe it would be less harm. I doubt that anybody who cracked the seed would move all at once. The effect would be obvious as you described.
But one question for me is: isn't it somehow priced in that the coins could move one day? I am saying somehow, not completely as it would still have an effect. But it would be naive to believe that they will never move again. It would cause some hands to freak out and sell. But it wouldn't make too much sense to me that Bitcoin drops like 50%.
I have never been convinced that the coins will never ever move again. I think they will and nobody even knows whether there is a good or bad soul behind those wallets. But that uncertainty exists already. Nobody can tell how many Bitcoin North Korea owns. An evil government could have been buying for more than a decade now and acquire a fortune at very little cost. This is more of a feature and who knows how much anonymous evil actors already contributed to Bitcoin's price increasing so much over the years?