Even though there are many varieties of mangoes , papayas and such, there is still room for improvement,
specially for commercial growers.
Of course productivity, and disease resistance are important , but customers also want taste and looks.
Other important features are shelf life, and recently things like evaporation weight loss, firmness, and the ability to maintain quality after quarantine treatments ( hot water dips , irradiation etc. )
Also changes in cultivation practices has given farmers the desire to have trees ( Mangoes for example ) that are more compact, for high density planting.
At the moment, Papaya farmers need a more resistant variety against PRSV, which is a major problem around the world. a solution that is not GMO based. this is where breeders could come in.
I was searching for the perfect commercial mango variety, and the closest I have come across is the Keitt, no surprise here, because this is the variety most farmers have had good success with.
But I feel, that the Keitt has room for improvement, mainly the fruit needs color, and taste can be improved on also. while maintaining all the good characteristics it has already,
Imagine a "Keitt" with the taste of an Edward, and the color of a Tommy Atkins. its really just not available now.
Avocado is another one that could be improved on.
For the back yard gardener , the needs will vary as much as the grower. obviously a mango with more cold tolerance would be welcome for US growers, Dwarf varieties, and such.