3rd edition contained addons for themes from the outer region - city, ruins, forest, crags, and the tower in the middle.
it looks like 4,5th ed will go that way again, larger then 3rd with three levels in the expansions rather then the two levels in the 3rd ed addons.
we know dozens more expansions, also those from middle region like castle. warlocks cave was a separat game when talsiman was very young. do you expect expansions beyond those from the 3rd edition and where shall be room for it ? in bath, in bedroom, in kitchen ? maybe expansions beyond the mainboard to be switched with ?