It seems to me, since I started following this game a couple summers ago, is that everyone wants Innsmouth. And I am sure FFG will comply, they would be foolish to ignore it.
However, I think Innsmouth may be the last big box expansion they do. That is why Kingsport slipped in first. I think people happily bought up Kingsport to tide them over until Innsmouth. But if they had been released in the other order, salesfor Kinsport might not have been so high and there would have been more cries that they are just trying to milk the line.
I don't know if there is anything else they would slip in before Innsmouth so it seems likely that will be the next expansion. I would think they may keep injecting small box expansions for as long as there is an interest.
If they want to do larger expansions after Innsmouth, I would hope they take the route of A Game of Thrones or War of the Rings and include basically a new game that uses components from the base game. My table can't hold AH, DH, and KH now, let alone IH later. But a separate board, like Mountainf of Madness, or expeditions to the Arctic or Europe or wherever would be a nice addition and probably bolster the line post-Innsmouth.