Exotic might not be the right word I'm looking for, but have you ever considered the market for more uncommon fruits? Not many people grow gooseberries, muscadines, currants, or pawpaw fruit.
I suspect that's partially because many people don't know about them, so the demand isn't high enough for large commercial production ....however, once people learn about them at farmer's markets or farm stands they may gain a consistent following (depending on the area).
I've read/heard in some areas pawpaws are starting to become rather popular at a local level.
Would that be depending on the region I suppose? I’m talking about North and South and such. Some fruits that are popular in the South could be considered too juicy in the North.