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It only requires a very short duration to send the difficulty permanently into the stratosphere. Only a fork can revert it. The attacker doesn't have any ongoing cost. The rental cost is cheap. All your CAPEX arguments fail because you forgot about renting.
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Incorrect. This is mounting a 51% attack for approximately one day in order to double the blocktime for approximately two days. I do find it interesting though when people suggest attacks that are way more expensive than a 51% attack and have relatively insignificant impact.