My copy of Miskatonic Horror arrived yesterday, some of the components seemed to suggest to me that there will be no more expanison boards for AH.
The Miskatonic University Institution namechecks all 3 expansions (Dunwich, Innsmouth and Kingsport) as locations that expeditions can be sent to, if FFG were planning more big box expansions wouldn't they have left this ability open ended instead of limiting it to the 3 known expansion boards?
The reference sheets contain information about monster and gate limits (etc.) for the number of investigators, each sheet also contains different limits depending on if Innsmouth and Dunwich are being used together or if all expansions are being used. It seemed odd that FFG would be able to assign values for 'all expansions' if they planned on releasing more big box expansions in the future as adding more boards would affect these limits.