There was an instructor I taught with at my first ski hill (pre snowboarders, they were banned on most hills then), that always took out a mono ski for fun when he got bored. His name was Mich. He used to ski on one ski half the time he was out on two.
Didn't really matter what ski or plank he was on, he was a neat skier and definitely skied to his own beat. We used to call him bird man cause he'd go down any run around on one ski with the other out perpendicular behind him and his arms spread out (wing like) in front of him. We often practiced coming down like it so 20 ski instructors could all come down in sync doing the bird man, lol. Haven't seen a mono ski since then.
Good memory of it though. I never had the desire to try it, and it looked really awkward. Was skied 70's Austrian style (feet side by side, locked into the binding), with the fluid back and fourth, arms high, graceful look.
Do I maybe remember seeing an altered version of one, with a rope on the front, in one of the first Warren Miller movies? Possibly that was more of a snow board, but I think i remember seeing one in an early miller film.