> Whilst the default length is 4 digits, you can change it to something longer if you choose.
Not really. You'll break international standards if you do. I used an 8-digit PIN for many years, but it is 100% impossible to use anywhere I tried in Europe. You will be completely without any way to pay other than cash. No machine will allow more than 4 digits in my experience.
How long ago was your experience? This may explain why (over the past 5-10 years or so) I've encountered more and more machines that require to press OK after entering the four digits (before, some machines would submit after you type the fourth, without confirmation).
It would be, were it not for the fact that the pin is randomly assigned. I've had a card issued with "2468" as the pin.
"I'd really like to see six to eight digit PINs, though..."
Whilst the default length is 4 digits, you can change it to something longer if you choose.