I'd also add that while perhaps a bit on the pessimistic side, I tend to view the 80 char rule / limit not as an ancient hardware limitation of monitors, but as a limitation of our eyes and visual processing circuitry. There is a reason why newspapers and well laid-out websites don't have 300 char width lines. Those are physically harder to read, whether we want to admit it or not, as our eyes lose track of the flow to the next line.

I'm all for decreasing unnecessary cognitive load, there should be quite enough of that without us adding more by accident.