I haven't made much progress on this project probably because I don't have a pressing need right now for a large cheap slow flip dot display. Mostly I was just noodling with ideas.  So I'm going to close this project for now.

If you are interested in pursuing this idea further you should check out : 

      https://hackaday.com/2021/06/24/mechanically-multiplexed-flip-dot/ 

Not only did James Bruton come up with the perfect name (Mechanically Multiplexed Flip- Dots) for the concept that 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.