Season 4 is going to be about Communism in the 1950s. The hint in Coven is the leader of the Witch Hunters saying he's have an easier time getting rid of Communists in the Senate than getting witches out of his hair. Ryan confirmed the 1950 timeline.
I don't have a lot of hope for the next season given that Ryan said if you liked the tone of this season, you'll really like the next season. This season fell apart halfway through and was just sadly a showcase of Ryan's typical laziness with a show as it goes on (see: Glee, Nip/Tuck). This season was not scary -- at least not beyond the first half -- and I wish they would take it back to the tone of the first two seasons.
that would've been amazing