I would like to use multiplexing with some tail lights, and my guess is that brightness will be an issue. I have no idea how im ever going to get around to it, but its still in the head scratching phase.
I think there are really too many factors to calculate things, the electronics stuff can be measured and calculated, but perception and biology are weird enough that I think you really have to test stuff to see how well it will actually work.
Tail lights that you can play pong or tetris on are just too fun to not try.