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.

University/Knowledge
Investigators: Amanda Sharpe, Rita Young, Mandy Thompson, Norman Withers
Monsters: Ghoul, Warlock
Scenarios: Something set on the Miskatonic University Campus

Museum/History
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
Monsters: Nightgaunt,

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

One thing is just about certain: a PoD expansion every two months (money in the bank, for ffg). I would love a box expansion twice a year. I wonder if the PoDs will incorporate the box expansions as they come or will it be more faithful to being mere additions to the core set (I care little either way, so long as at least one PoD addition incorporates the newest expansion each time). As well, I am reading now Lovecraft's fiction. I am a third through his complete works thus far. For now, it would seem a castle/dungeon expansion seems likely, but I also could see because of Red Hook and other urban horror stories of his that Mansions could lead out into the streets.

Something I am eager to the idea of is FFG making an Ancient One figurine the size of a square TILE (make a Shoggoth crawl back into the hole where it came from), with a PoD expansion included. The utter rediculousness of an epic boss fight and getting chased around the board by a behemoth is something I would pay to see (affordable too would be great; those who want to paint, do so, and those who want limited edition can pay more). A nice protective box for both figurine and protective divider for the PoD expansion sheets would be definitely appreciated too.

I also am almost finished writing up my first custom map, so a contest for a PoD publishing would be utter madness

maybe not that big, I do have to store these things somewhere lol. But a Cthulhu star spawn, the king in yellow, or maybe one of the black goats young would definately be cool.

So with the new Monster Figures announced, we can probably assume that the next Big Box expansion will probably be Dunwich/Black Goat of the Woods themed. Along with the existing monsters they also have Dark Young, Dark Druid, Goat Spawn, Child of Goat, Wizard Whatley, The Dunwich Horror, and Hunting Horror? (hmm doesn't quite fit the theme, but whatever...)

If Forbidden Alchemy is the equivalent of AH's small box expansions (2 monsters, 3 scenarios) I'd expect the Dunwich expansion to be the same size as the base box, (assuming we get all those monsters at once.) It'll probably feature several outdoorsy tile locations like Sentinel Hill, a ruined farmhouse, the Dark Forest, a sacrificial altar, etc.

On another note, I certainly hope at least a couple PoD expansions after FA make use of elements from the expansion, especially the puzzle types. I think it'd make sense if each expansion had one or two PoD scenarios following it up. Be a shame otherwise.