Before I start, I'd like to say that I won't be talking about the theories we've all heard, such as AHS: Apocalypse or AHS: Orphanage.
Anyways, my idea is that the season will take place in or around the Bridgewater Triangle. For anyone who doesn't know what that is, it's an area in southeastern Massachusetts with many reports of paranormal activity, including poltergeists, UFOs, and balls of fire dating back to precolonial times.
There's many reasons I feel this could have something to do with next season's theme. My first idea is the fact it's located in Massachusetts. The state has appeared in all 5 seasons (e.g. Coven took place in Salem, the Harmon family is from Boston), so why would it not be in season 6?
Secondly, the Bridgewater Triangle could give a story for both the past and present. Next season is suppose to take place in both timeframes, so it fits perfectly. The past could show the events causing all of the paranormal phenomena, whereas the present day part could possibly have people exploring the Triangle.
The next one is probably the most convincing. I recall Murphy saying clues for the theme were in Murder House. I'm not sure if this was just a rumor since I haven't heard anything about it for a while, but just incase it wasn't I'll use the statement as proof. In season 1, Billie Dean Howard mentions that the Native Americans used a curse on the European immigrants. Allegedly, the same thing happened at the Bridgewater Triangle. Along with that, the 2 stories share a couple similarities: they both start with the Colonial settlers giving the Natives poor treatment, then they curse an object to get back at them.
Finally, we all remember hearing about how season 6 will focus on children. However, Hotel also focused on children, but there was only about 15 kids who didn't do much for the plot. Therefore, we'll likely see the same amount of children next season, which means the whole season won't revolve around kids, like a school or camp. Anyways, my idea for this one is that the children in the series could be either ghosts due to the many homicides in the Bridgewater Triangle or one of the main character's kids.
But something I can't figure out is what the subtitle is. I looked into the Triangle's past, but the best I could do was American Horror Story: Graveyard or a popular idea, American Horror Story: Cult. What do you think it could be? My guess is as good as yours.