And miners can request KYC information to be submitted alongside their transaction too, but you don't see that happening

It's 2026. The feds decree that bitcoin miners and fedimint operators are both money transmitters whose customers are "anyone sending bitcoin using that fedimint or in that miner's block." Therefore, they cannot lawfully mine bitcoin or run fedimints without obtaining kyc data from senders. When the law takes effect, alas, 10% of bitcoin users, including fedimint users, have not adopted wallets that submit kyc data to miners and fedimint operators alongside transactions.

Mining pool operators in the USA therefore begin excluding such transactions from their blocks, and fedimint operators transfer full control of all user funds to new multisigs where none of the keyholders are known/public residents of the USA (because very few operators are willing to get arrested, and the few who are, are ejected from the multisig by the other multisig keyholders on the grounds that it would be disruptive to their operations for a critical team member and keyholder to get arrested and not be able to sign transactions anymore). Mining pools in other jurisdictions show a marked increase in profitability since they are mining more transactions than those in the USA, and individual miners begin pointing their hashrate at the more profitable pools.

Fedimint usage also continues unabated, with the sole tradeoff being, multisig keyholders are only people who (1) don't plan to travel to the USA, where they are criminals, or (2) think they can keep their keyholder status secret from the USA government.

The percentage of hashrate owned by USA mining pools drops, and bitcoin continues operating as usual, with no KYC requirements. Basically, mining pools and fedimint operators all effectively left the USA or went underground, but regular users of both systems are unaffected.