For new ag machinery, embedded control systems are absolutely essential for the machine to do its job. The ECU on the engine is generally reliable and have long life. The other stuff, I'm highly dubious of the long-term maintainability of it. On our farm, we ran a lot of older equipment and did a lot of repairs ourselves. For new equipment, that will be near impossible as the electronic control systems are black boxes. Even the cabling is complicated and is generally not documented. After the machine gets a decade or two old, good luck fixing it.
I suppose you could just drive the machine in the junk pile. However, when a new combine harvester is costing around 3/4 of a million USD, that seems a bit wasteful. I don't know what the solution is though. The farmers buying new equipment don't care so much, their resale value is not suffering too badly. The manufacturers are looking for ways to sell new equipment and adding more features via electronic controls is a relatively cheap way to enhance the product.
Most farmers say they don't want all these new electronics on their machines. When Deere announced their S700 series combines, they had a video bragging about all the new improvements:
If you study it, you will notice that most of the new features are due to software changes or to electronic control systems. Little of what the machine actually does to harvest the grain has changed (metal parts, etc). This automation features are nice when they work but are a disaster when something goes wrong. The operator will have trouble to determine what the machine is doing (never mind trying to figure out how to fix it).
However, even though many farmers say they don't want it, the new machines are selling well. So, maybe you could argue the market is working. To me, it feels like there could be some externalization of costs going on. These new machines are very much less valuable as they get older vs the previous era of farm equipment. I guess the same thing has happened to automobiles. You can take a car from the 1940s and fix it up into perfect condition. If you take a 2017 car loaded with electronics, would you have any hope of fixing it to new condition in 50 years from now?