This was posted to the blog about a month ago: https://hackaday.com/2021/06/24/mechanically-multiplexed-flip-dot/. Not only did James Bruton come up with the perfect name for the concept I have been trying to explore hare, he has produced a much more fully realized demonstration of how it would work with his 5 x 3 ping pong ball display. 

But the idea is the same. The 15 dots are controlled by only 3 servos and 1 continuous motor to move them across the display. Slow but relatively cheap. So cool.