computers, yes. High-end electronics, beats me. Not on the list but state of the art electronics most definitely.
The new electronics that does stuff like run lights and relays have the ability to see if the wiring is OK. If the bulb is blown or the wiring is cut, it can detect that. When the device is off, it puts out a very small current to see that the wiring is OK. If you short the line to ground or plus, it can tell there is a short and does not pop a fuse because the electronics that drives the line is current limited. So it's pretty nice- you know you have a problem before it bites you, having the problem does not take out other systems, and the exact nature of the problem is known.
Now to take advantage of this, the various computers have to talk to each other so that the operator display can let you know what the problem is. So we have good and bad sides to it all. More complexity, but better diagnostics. I do object to the information that the computer system know not being made directly available to the owner of the tractor. It's as cheezy as when there were "special manufacturers tools" you had to have to work on stuff. And of course the computers certainly help in meeting the emission standards.
Now as for reliability, I remember being interviewed when I got out of school in the late 70's by an automobile manufacturer that was getting more and more into computer control. So in 30 some years a lot of the bugs have been worked out. Put another way, we are at a point where failures are more likely to be the result of stupid cost reductions than core technology unknowns.
As for spare parts, my Deere has a box that houses the transmission controller, and another for the display. That box has the circuit board with the computer and other electronics on it, and several connectors that have water tight boots on them, and the connectors themselves have the pins water tight. When you look at the tech manual, there are extra pins on the connectors. So if the chips used on the circuit board go obsolete, the manufacture can cut a new circuit board and port over the software. There is nothing to keep them from using a handful of different board designs over a large number of tractor models. In fact, there are as many different good reasons for doing that as there are for using the same engine block in a variety of tractors.
So the matter of "will you have spares in 20 years" is not a technical issues, but a management issue. Did the company keep using it's core form factor (box size and connector type/pinout) so they could keep the design up to date? Did the hardware and software guys make the software so it can port over to faster processors without any major re-work? Time will tell.
Yes, I'm biased on this too... We all like to see thing implemented in technologies we can work with or understand

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Pete