I am considering multi fruited trees. These are trees that different fruit cultivars are grafted onto one root stock. This means that the tree produces different types of fruits on different branches. Benefits include saving the space that a would be required to plant separate trees, the ability to get trees that can pollinate themselves, and a longer harvest time as different cultivars produce fruit at different times.
Of course there are potential problems. Pruning can be extra work to make sure a single cultivar doesn't take over. The total yield of fruit most likely will not be more, just spread out over time. Also, some cultivars on the tree might be more prone to certain diseases and pests than others. It could be difficult to safely treat a pest or disease that is only present on parts of the tree. Another aspect is price - multi fruited trees can be expensive. Finally, the exact interaction of the cultivars is hard to predict. Will one cultivar hog resources? The fruit might taste good but without much analysis it is hard to know for sure that the nutritional content is just as good as trees grown individually.
A store I found that doesn't say "cannot ship to CA" is Nature Hills Nursery . I am really excited about this website. They have a multi-fruited / multi-budded apple tree with a description that recommends planting in zones 4-9. I think I would like this tree. It produces 4 different types of apples. That is great so I don't get too tired of any one type - or end up with a too many apples at one time.
The website also sells two different multi fruited pear trees. The one that is hardy in my zone, "Multi-Fruited Pear Tree 1" grows 4 cultivars. I would like this tree as it grows Bosc pears - my favorite pears for their sweet flavors.
The website's multi fruited cherry tree does not include my zone in the planting recommendations. I might plant it anyway near other trees so that they can create a cooler microclimate. Cherries are so good - but so expensive! It would be great to have my own.
I do not know whether I would put fruit trees in the front yard since they drop a lot of fruit that can be a bit unsightly on such a beautiful street. That can be a lot of fruit to pick up! I would not be able to plant multi fruited trees along borders in my front yard since it is very important for all the cultivars to receive adequate sun. In the backyard I could just rake up the dropped fruit and easily put it into the compost bin. That is less work and more forgiving when I miss a few days of upkeep.
A final factor is cost. These trees are more expensive than trees that haven't been grafted. I do not necessarily need 4 different types of one fruit. I might need at least two different types so that they can pollinate each other. Two trees might be less expensive than one multi-fruited tree. Extra care will need to be taken to choose cultivars that bloom at the same time. Then there is the cost to water the plants. One tree likely requires less water than two separate trees, a benefit of having a multi fruited tree. Finally, there is the issue of space. Planting only one tree means that space is available for other crops. A packet of seeds usually costs less than a tree. Then seeds can be saved from the crops, so that only one investment into seed packets can last many years.
I think I might order some multi fruited/ multi-budded trees when my soil is ready and the climate is right. I also plan to get some traditional fruit trees that are self-pollinating. There are many options. Multi fruited trees are a lot of work to prune to make sure all the cultivars are getting light and to keep the tree balanced. Any tree will either need to be naturally short or pruned to keep them from hitting the power lines.
Other options? Give a pollinator tree to a nearby neighbor. You get pollinated, they get pollinated, and you both get fruit. There is also the option of grafting your own cultivars onto a similar fruit tree you already have. You can get the cutting from a friend, or grow the new tree and give it away after you have produced a graph. I certainly like this option, it gives more than one home something they could use and beautifies the neighborhood.