I made this with cardboard on Thursday Thanksgiving day as a prototype, just to see if it is possible.
Now I have it in QCAD.Top layer:
For Filco Tenkeyless, this layer needs to be thicker to raise the top layer higher because of Filco's controller. This layer can be thinner for Phantom since its controller is under the PCB:
Cut out for Phantom's controller on the left, Filco's 5-pin plug on the right, plus cable routing. I need to know how much the Teensy controller stick out from the keyboard PCB because I can tell how thick this layer need to me.
The bottom layer:
If it is made with transparent acrylic and you look at it through the bottom layout, it would like like this:
Hum, I think I need to move a screw hole...
EDIT: Added a screw hole, and now a 7bit top layer: