This is me throwing ideas at the page to see what sticks:

1. Addressable LEDs driven by a Teensy3, then networked by a Raspberry Pi? The Pi can be the network stack and the Teensy can drive the segments. Effectively frontware and backware. How to talk between?
2. Lasercut segments and “holder” for the segments. White perspex for the segments. MDF painted black for the holder.
3. cheshire to design and lay out the physical layer (Will attach PDFs when done)
4. 7 digits. Allows us to count to 9 Million.
5. 16 segment “Union Jack” allows us to scroll text back and forward. “rennapS a htiW retsiS ruoY lliK”?
6. 3 layer design. Upper layer is black painted MDF “Mask” and White Perspex “Segments”. Middle layer is white painted MDF “airgap” with marginally smaller versions of the segments. This makes assembly easier and gives us some more dispersal on the LED light. Bottom layer is white painted mdf. It's got holes cut to hold the LEDs nicely in place to make construction easier.
7. There'll be a wooden frame to hold this all together at the end. I envision 4 pieces of pine with 45º cuts in the corners with a routed channel to hold the layers nicely together. (Insert illustration here)

Here is the 3 layers, ready to be cut with the big laser counter1.dxf.zip
Here are the segments ready to be cut with the small laser counter1segments.dxf.zip