I expect that it will continue to be the preferred mechanism for paying criminals. It genuinely improves on the experience for both criminal and victim vs alternatives like wire transfers and cash. There is a decently large market for paying criminals (illegally but also legally, eg ransomware), so some base level can be expected to continue.
Law enforcement and private surveillance companies are currently investing a ton of effort into using public blockchains (which is most of them) to unmask participants in crypto transactions. At the same time, they're putting more pressure on Coinbase and friends to do aggressive KYC, and Congress keeps considering bills that would effectively outlaw anonymous crypto purchases. It's not going to be the safest way to collect ransoms for long, if it even is today.
