Breeding apples is hard work. It takes 5 years to produce fruit from seed and you can't even cross them with close relatives.* Despite the difficulty of developing new varieties, there's already an incredible diversity of growth habits and fruit types in wild and domesticated apples, but almost all our commercial varieties are simply grafted clones that some lucky farmer found growing on his land. Today, only 11 such clones account for more than 90% of apples sold in the U.S.
Even easy improvements to apple varieties (e.g. introgressing a new resistance gene from a wild relative) generally takes two decades. It's all but impossible to make more complex changes (e.g. fruit quality) within one person's career. But there may be a shortcut...
A poplar tree gene has been discovered that causes fruit tree seedlings to grow green and slouchy - but produce fruit in less than a year. Scientists, including some at the Appalachian Fruit Research Station, have hatched a plan - they're going to genetically engineer this gene into apple varieties. This will allow them to cross different wild and domesticated apple varieties and select improved offspring (with marker-assisted breeding) almost as fast as you can in corn! During early cycles they'll select for offspring with the fast-flowering transgene in addition to fruit quality traits. Once they have the fruit traits they want, they'll simply select an offspring that doesn't contain the transgene and presto! A healthy apple tree with novel fruit quality traits in a few years instead of decades!
h/t: Besting Johnny Appleseed
*Apples have some degree of self-incompatibility that prevents establishment of pollen grains that share too much genetic similarity with the mother plant. Kinda like our antibody-mediated immune system, plants produce proteins that recognize whether pollen is closely or distantly related (if the matching proteins are the same or different). I'm not sure if apples are obligate outcrossers (e.g. can never self-pollinate), but it's apparently enough to slow breeding.