At least officially, Jim Bell (author of the Assassination Politics essay) was not imprisoned for writing that essay, he was sentenced for tax evasion and using fraudulent SSNs. I'm sure they investigated him after publishing the essay, and charged him with what they could, but his 1A rights weren't violated.

In general you're not allowed to advocate for violent overthrow of the US government, but I think decentralized prediction markets are abstract enough a concept (no material actions/threats against individuals) that it'd still be protected speech.