It occurs to me that it might be possible to use the Arkham Horror board(s) with Mansions in an effort to develop new scenarios. Using the AH board as the "Big Map", and then zooming into a location using the Mansions tiles as the "Detailed" view. It would still play as Mansions, but give you a much larger landscape to work with. You would put together mini-encounters at certain locations, with clues to the overall objective, that would eventually lead players to the climax location to stop whatever cataclysm is occurring.
Not every AH location would have encounters, some could simply be closed and this would be identified on the board with a token, so players wouldn't waste their time in those locations. Some could simply be there to be used for the benefit of the players (or possibly the keeper too, we'll see) like buying new equipment at the shop, or healing at the hospital, or searching for ancient tomes in the library. They could either have a paragraph describing the location with what actions are available there, or move into a zoomed view with the Mansion tiles, so the players could search there for clues.
Players turns would still be 2 movements and an action, the keeper could summon to the big board as well as the small ones. There are many possibilities, and it would probably need a few regular Mansions expansions in order to pull it off (so that you have more rooms and more monsters to work with) but with scenarios designed properly you could pull off an amazing game, I think. I’m going to have to flesh it out, there are obstacles to overcome, any thoughts?