In my experience Fantasy Flight Games like most developers tend to develop their games from a certain formula and ive been pondering if we havent seen enough to determine roughly how future releases will look like from what we know of the expansions so far. So Im going to indulge in some speculation here.
First of I think we can assume about 3 print on demand scenarios inbetween expansions, atleast if sales on them keep steady. They arent to tough to crank out and I think there are plenty of "guest writers" interested in coming in and just doing a scenario. Also I wouldnt be suprised if they eventually hold a contest where fans submit scenarios and the best get to be chosen for a PoD.
Large box expansions seem to be based upon location types or themes with the first one being laboratories/science (depending on how you interprete it) .They will most likely all contain 4 investigators, 3 stories and 2 new monsters each. Not sure if they will all contain 1 new puzzle type but I hope so. Most FFG expansions seem to introduce a new game mechanic, so Alchemy Puzzles might just be Forbidden Alchemy´s unique mechanic and future ones might have new ones that in no way are puzzles.
The part that I allways find the most interesting ofcourse is to try to guess what future products will be released and how they will be connected.
As for PoD stories its hard to tell, pretty much anything could be done but one could speculate quite a bit in the box expansion area.
If things keep after formula im going to guess expansions along the following lines.
Investigators: Amanda Sharpe, Rita Young, Mandy Thompson, Norman Withers
Monsters: Ghoul, Warlock
Scenarios: Something set on the Miskatonic University Campus
Investigators: Monterey Jack, Ursula Downs, Leo Anderson,
Monsters: Mummy, Serpent People
Scenarios: Something based on the Black Pharaoh
An Innsmouth expansion (Not sure what theme or location it would be based of, but its pretty much a given in some way. Perhaps based of Warhouses and waterfront locations, or abandoned buildings or industry)
Investigators: Silas Marsh, Zoey Samaras,
Monsters: Deep One, Deep One Hybrid
Countryside (farm/dunwich) /
Investigators: Hank Samson
Monsters: Goat-spawn, Dark Druid
Scenarios: Something based on the Dunwich Horror
Personally I would also like expansions based on other worlds, perhaps an expansion based on the dreamsdreamlands
Investigators: Jacqueline Fine, Luke Robinson, Patrice Hathaway, Lola Hayes
One monster however is more or less confirmed already, and that is the Vampire. Since it is mentioned in a card. However, I dont necisarily think it will come anytime soon since I expect they put that text in as a precaution and will want to release more iconic Cthlhu mythos creatures first before falling back on more mainstream monsters like vampires.
Well, enough speculation from my end for a day, hope some of my ranting made sense