Is It the Last Word?
In State v. Rainold, the Oregon Supreme Court looked at the felon in possession statute and concluded that no mental state applied to the defendant's status as a felon. So, we have a state statute interpreted by the state supreme court. Short of a legislative amendment (which seems unlikely), it's hard to imagine this isn't the last word on the subject.
Or it was hard to imagine until I saw portions of a federal opinion (or more specifically, portions of a concurrence) at Sentencing Law and Policy blog. The post is here. At this point, I'd say it's highly theoretical, and nothing will change (in state or federal court) unless SCOTUS decides to weigh in. But it is possible Rainoldi might not be the final word on the subject.