Israel in particular has spent a fortune on research into robotizing fruit production, since they have money but have complex relations with neighbours that make cheap labour immigration unreliable. They are working very hard on all the literal hanging fruit.
The problem is that a farm is a dirty, corrosive, and stochastic place.
Equipment needs to be tough as nails and able to deal with each unique farmers challenges.
Things I see on the horizon :
Robotic weeding is going to be a HUGE deal. Improved robotic harvesting also. These both are almost entirely reliant on robust computer vision that can survive days in the field.
Drones are going to also be a huge deal. Imagine a quad copter that can go out and sample your 1000 hectares of fields, spotting disease or nutrient deficiency from images taken from above.
The promise is big, but integrating tech seamlessly is going to be damn hard.
I believe that one is already a reality. Some quick Googling turns up: http://www.precisiondrone.com/drones-for-agriculture.html I'm pretty sure I saw a TV special too.
I'm sure that there are areas to be improved upon, but I expect a lot of the low hanging fruit has been picked, as it were.
I also tend to think of farmers as the original hackers, they often have problems, and they cobble together a solution that might not be pretty, but works.
Once I finished some other projects I'll looking into Arduino or something similar to start hacking at some ideas I have.
By the way, you are indeed right that farmers have already done most of the hacking themselves.
I have/had a few ideas I was researching and at least one I plan on testing on my own acreage this summer. Figuring out how to market to a population that doesn't seem to have a big online presence is the hurdle I haven't crossed yet.
One of the things that I'm looking at (as a hobby research topic) are automating managed intensive rotational grazing for cattle and remote herd management.
Surely, these projects sow the seeds of eventual progress.