I am not an attorney, but I think that the laws about the statute of limitations are different for a conspiracy than for an individual crime. RussiaGate was clearly a conspiracy.
I always wanted it called a conspiracy and not a hoax. The word hoax implies a bit of levity, and there is nothing funny about trying to overthrow the will of the people.
I think you are right, no statute of limitations when it comes to conspiracy to commit sedition or treason.