One other thing to consider, which has been mentioned before, is what if FFG could come up with a board based expansion never done before. That would be something to distinguish 4ER as more than a remake or upgrade from previous editions. That would be something to keep sales stronger longer. Especially if it were released in the middle of other scheduled releases already being discussed instead of after all other remakes of known board based expansions for any edition. But personally, I just not sure what there is one that could be done wholly new that would have wide appeal. The past boards, between a mix of 2E and 3E already cover the most feasible and broadly appealing concepts already.
I have heard of notions to expand other spaces into regions... oops, I mean "realms." And based on several differing fan expansions there were notions metioned for a ring of "seas" around the board. But beyond these and the previous realms, I'm hard pressed to think of anything else? Has Talisman, based on its FULL history of expansions, reached its FEASIBLE limit for expansion boards?
In addition, there's the physical space challenge. If the four realms are (re)created, where could one possibly put anything else? Overlays are another possibility, but that again is something Talisman has already seen. What do you see as possibilities that would (1) have a wide appeal, (2) not supercede other popular expansion boards waiting to be recreated, and (3) able to to interact compatibly with previous or future standard recreations?