Wow! Why so complicated? Just, as you say, overkill. We have a canbus and we are going to use it!
Here is a devious one for you, just one more actually engineered to break on purpose.
Dodge Ram Cummins with automatic trans and it’s own Trans computer. The computer software has overheat sensors and “derate” type protection in place. The sequence of control if it starts to overheat is to first kick it out of overdrive without any other indicators, then it kicks it’s self into neutral with no other indicators, then after a bit the red overheat warning light finally lights up last to let the driver know that the reason it has already done those previous is because it is overheating.
Now why doesn’t the red warning light indicator come on FIRST before starting to go through the physical self protection sequence?
So, a common thing to happen with these is the pin connectors on the trans temp sensor are very small pin connectors. After a few thousand miles these connectors get loose and can break contact inside the connector housing intermittently causing a brief open circuit. Because of this quick break in contact it makes the computer go through the whole self protection sequence, Kicks out of overdrive, and kicks into neutral, but it resets before the overheat light actually comes on.
This starts happening every time you hit a hard bump causing the connection to open a slip second. But it never does get to the point that the warning light comes on to alert you that the issue might be part of the trans temp sensor or wiring to that sensor. Because it was programmed to come on LAST rather than FIRST in the sequence. So the first thing that comes to mind for the driver is that the trans is actually failing, and repair shops are NOT going to argue, and will agree with the driver because it is big money for them.
I know for a fact that thousands of transmissions were replaced that did not need to be replaced because of how this sequence was programmed in, when a simple easy to fix loose connector terminal and the computer sequence was actually the problem. If the warning light came on first in the sequence instead of last, this would have prevented all of it.