On using robots to make gardening scalable to millions of acres...
You might wonder why I want to turn land management over to robots. Is it because I'm such a geek that I think everything goes better with robots? No, not really. Sure, I think the technology is cool, but I'm not eager to factor human beings altogether out of any activity, not even those that are dull, dirty, and/or dangerous.
I am, however, eager to see the benefits of replacing methods designed to spread a human operator's time as thinly as possible with methods which reintroduce attention to detail to plant cultivation. Granted, that attention would, for the most part, be provided by robotic sensors, processors, and algorithms, but that has an upside as well as a downside.
The downside is mainly that it's unfamiliar and we don't know whether we can trust it. The upside is that robots aren't limited to human senses, but can go as far beyond them as available technology will support, providing information not directly available to us, and they also aren't limited to the time a human operator can afford to invest, provided they are capable of autonomous operation. Potentially this means that instead of a single machine running 40-60 hours per week, you can have many machines running 24/7, vastly increasing the available machine time per land area.
Combine that rich sensory information and machine time availability with manipulators capable of performing basic gardening operations (planting, weeding, pruning, harvesting, saving seed, ...) and you have a platform justifying the effort to develop higher level software which supervises beneficial plant combinations in space (polyculture) and time (crop rotation), which is capable of mixing annuals with perennials (permaculture), which makes room for native plants (particularly those that are threatened or endangered), which also makes room for animals without allowing them to ruin crops, and which can make sure there are enough flowers, throughout the season, to keep pollinators healthy.
Such a system could also learn from experience, even setting up intentional experiments, maintain the genetic diversity of crops, and accelerate the creation of new strains in response to changing conditions. It could also provide exquisitely detailed information in support of operation management.
Technology of this sort would make for a far more varied and interesting landscape (biodiversity) and greater variety of production (diversified income), supporting a more well balanced diet for those dependent upon it. It could also dramatically reduce the energy and other inputs used in crop production, all but eliminate soil erosion and the airborne dust and stream contamination that result, reverse the loss of organic matter in the soil (improving its water absorption and retention and contributing to the sequestration of atmospheric carbon), save many endangered species from the brink of extinction, and bring the practice of agriculture into parity with other aspects of the modern world in its sophistication and the respect it commands, helping to enhance rural culture.
So, yes, that would be very cool technology, but it's really about all of the benefits that could be realized through its widespread deployment.