> Civil forfeiture is dependent on being able to "prosecute" your stuff, rather than you. So if they can't seize it, they have to go after you directly.

The US certainly has had cases prosecuting "stuff" where said stuff is cryptocurrency. See "United States v. 178.95842915 Bitcoins" [0], which appears to be a civil forfeiture case [1][2].

[0] https://www.usmarshals.gov/assets/2016/bitcoinauction/index....

[1] https://www.pacermonitor.com/public/case/10752506/United_Sta...

[2] https://docs.justia.com/cases/federal/district-courts/washin...