Trickster Spirit
Explorer
It does leave things open, but I also think that until they put out one of their twice yearly storylines without an associated AP book(s), it's fair to expect two AP per year.
So do I, I'm just pointing out that they've only ever spoken about "future storylines for D&D" - they've never explicitly stated that there will be two APs a year, or even any tabletop RPG products at all after Princes of the Apocalypse. I mean, you know what happens when you assume...