I wouldn't say they were entirely replaced. 4chan always had a libertarian disposition, which left the door wide open for the reactionaries to make themselves at home. Libertarians have a keen eye for identifying the deterioration of society, but they have no systemic conception of power, and no answers. Meanwhile the fascists are willing to spin any story and blame any scapegoat to explain the alienation of a generation of petit bourgeois failsons. The dimwits on 4chan swallowed it hook line and sinker.