Has anyone actually been prosecuted over a “non-custodial” model?

Yes, and the results ended the debate. In United States v. Storm (S.D.N.Y.), the court held in September 2024 that a service can qualify as a money transmitter under 18 U.S.C. § 1960 regardless of whether its operators had custody of user funds; the jury convicted the Tornado Cash co-founder in August 2025. The Samourai Wallet founders pleaded guilty in July 2025 and received prison sentences of five and four years, with a $237M forfeiture — for a wallet where funds never left the users’ keys. BTC-e’s $110M penalty established that offshore incorporation while serving US customers changes nothing. Note also that operating without a required state license is a federal felony “whether or not the defendant knew that the operation was required to be licensed.” (18 U.S.C. § 1960(b)(1)(A), (C))