Are there any other popular theories out there yet?
Nothing super promising. Some viewers have been wondering if the references to Butte at the end of Cult were hinting at an eventual trip to Montana next season -- perhaps to tackle the city's early mining days. Some believe Cult's regal references and repeated use of the word "revolution" could be a sign the show is jumping back in time to the American Revolution, though that's in direct conflict with Murphy's intent to set this season in the near-ish future.
Others have been revisiting the popular Inferno theory, which Murphy teased before Cult premiered, for clues. (See above and here.) Given the crossover news, we think the Inferno material has the best chance of rearing its head. First popularized by TV site Red Herry, the Inferno theory angles "each season of American Horror Story as a 21st-century interpretation of a circle of Hell" -- referenced in the first part of The Divine Comedy, Dante Alighieri's 14th-century epic poem that you probably read in high school. Murphy has yet to officially confirm the theory, but he does like it! If it's legit, it could hold major clues about the crimes, punishments, big bads, and themes to come (see: Lust, Violence).
Wait, so ALL this is happening in Season 8?
You'd be right to be a little suspicious. For starters, this is Ryan Murphy we're talking about -- fans will no doubt remember the innumerable red herrings that littered the run-up to Roanoke. Also, around January of this year, when all these clues started dropping, Murphy had told EW that Season 8 would not be the crossover season. ("It'll probably be the one after [Season 8]," he said, citing scheduling conflicts -- namely, Bates, whose Netflix show, Disjointed, had yet to be canceled. "We've already met about it and outlined it, but it won’t be next, because some of the people are not available.")
So... how does the crossover news reversal, which came almost half a year later, change things? There's been no indication it will, but Murphy also hasn't clarified this yet, so it's unclear which of the above pieces of info will get tweaked, stay the same, or be shelved until Season 9. If we're using Collins' first cast picture above as a reference point, it seems like most of the developments listed above, especially the bits that have come since March and April, have stuck. (Production is supposed to be under way already, after all.)
If anything big changes, or if we get any clarification, we'll update this post -- stay tuned.