This is a post I wanted to think about some time, here are my thoughts.
Some well known fruits have a lot of potential for growth in the market, the mango that we all take for granted here. is still an exotic in many parts of the country, and most people only have access to maybe one or two varieties.
The "trick" with mango in the US, would be to take advantage of latitudes north of Mexico, and very late season varieties, so you can meet the demand as Mexican production falls. if one was to use UHD ( Ultra High Density ) planting, production in smaller areas can be had.
Almost anything could have a niche market. many tropical Asian veggies could be grown for restaurants, or ethnic markets. one off the top of may head, would be "Bitter Melon" not only for the food market but also for health food supplement market.
Also the tendency in the US is for prepared products, so if you grow something and process it in some way, your chances of success and profits will increase. here i can think of Lucuma, Lucuma powder is being used in cooking, but is being imported from South America and is pretty expensive. In S.A. Nestle even has a Lucuma flavored ice cream being produced commercially, and is the preferred flavor by some of the locals. I see no reason why someone somewhere in the US with appropriate climate could not grow these, for making lucuma powder.
Improved varieties of almost any fruit or veggie has potential. as mentioned already Pitaya has a lot of room for growth.
all the above ideas are for "commercial" crops. for the backyard grower, anything goes really. from Blue corn, to Ecliptica alba.
Something doesn't have to be accepted by the masses like bananas to be a success, speaking of which, what percentage of the population you think has tried a manzano banana ? how many do you think would switch to manzano over those tasteless varieties sold in supermarkets if they had access to them?
For the D.R. some future crops for export, Mangosteen i see as having a good market.
One other fruit , with good success potential, is the "Jagua" has a unique liqueur flavor, some medicinal properties, but its biggest potential is in the temporary tattoo market, for its natural dye. already one company in S. A. is taking advantage of this.
https://www.youtube.com/watch?v=-ZMmqWS9brUOther Interesting fruits and plants
Camu Camu
Diesel Tree
Yacon
Some Garcinias
Argan ( For Oil ).