If the current releases are any indication, we'll get a big box next (maybe Lovecraft Country, which is a great suggestion from someone?), followed by a small box.
Those could continue the 8-investigator (big) and 4-investigator (small) releases we have to date...meaning that with one more big and one more small, we should be up to the 48 investigators we've seen forever in FFG Arkham products.
Maybe then they release a Miskatonic Horror-type expansion and we're done with EH?
Just speculation. The decks are already getting unwieldy...GOO-related ones notwithstanding.