I did it once in March 2007.
I did ride rides in all 4 parks, but you have to be very surgical in your choices and you’re going to be dead by the time you return to your car. And it helps to be by yourself. If you have to pace yourself to a slower walker, you won’t do it.
I arrived at 9:30 at the TTC lot, hit all 4 parks, and actually returned to the MK by 7 with the intention of meeting some friends who were having a birthday dinner at Crystal Palace.
I made it, but they were already seated. The CMs at Crystal Palace let me in to join them, even though I wasn’t eating. I could have if I’d wanted, but didn’t. I did plan to simply say goodbye, but wound up talking while they ate right up until Wishes at 9 PM. And again, this was one of the few times I hadn’t planned to stay for fireworks.
PS: For this exercise, Disney Transport is your friend.
PPS: This was a day trip, so there were three hour 200 mile drives beside a full day in the parks. They were doing a passholder preview for The Laugh Floor and I was even chosen as “that guy”. That makes me one of the very first “that guys”.