"Tropical fruit" is, like someone else mentioned, widely available and you can pick and choose the fruit for their ripeness based on when you'll need it. Perhaps one advantage you could offer customers is a service with local farmers who are producing organic fruit (dragon fruit, longan, rose apples, lychee, bananas, papayas). Since it would be difficult to have a steady supply, perhaps even find some reliable, organic distributors from China. Just the other day I saw a rose apple tree on Peng Chau FULL of fruit that was going to waste!
I wouldn't use an online fruit delivery service, but if you were offering this advantage, I would consider it!
I agree with another poster -- if you could find a way to bring this to those living abroad it would be better!