Ball bearing dot matrix
I prefer the flip-display solution, but here's another alternative. Metal grids are quite cheaply available and if laid flat, ball bearings will stay in the hole they're placed upon. A ball bearing can block light, or alternatively, glass marbles could be used which can focus light to a display or refract it in other ways.
The advantage would be that the grid and the ball bearings are cheap stock components, so you wouldn't have to manufacture each bit. You would have to make the device for pushing ball bearings (and reading their position if you want to read out) but that would hopefully only be made once per word, column or so on.
I'd imagine you would not add or remove ball bearings from the grid, but just shunt one bearing between a '0' row and an '1' row per bit, with the 0 row not being visible to the user.
Biting the hand that feeds IT
