I'm not great at following schematics but I think I see what you're doing there and it looks like an elegant solution.
The schematics will give you a headache.
I couldn't come up with a schematic representation that made sense, and I get paid to make schematics that make sense! And if you think this is bad... The Enter Zero key will be even wilder.
What I will do, though, is add a silkscreen guide to the PCB itself that shows wire jumper configs. "Do this if you want a 2U."
Ok so i'm still a little confused... you're saying this will be 2 pcbs that can be used as a split board, combined as a full expanded board, or physically cut with a saw along your indicated lines and still works as something smaller? and its dirt cheap?
Symmetry is awesome, isn't it?
This all works because it needs a plate to give stability.
The Teensy++ mounting is tricky due to clearance and orientation issues. I have 5mm clearance, with 1.5mm eaten by the plate. That gives me 3.5mm between the plate and the PCB. The Teensy's USB port alone is 4mm tall. Thus, the Teensy needs to be mounted on the opposite side of the switches or it won't fit. This works for the left half (and the primary half of the full single-Teensy keyboard). But the right half has issues. The right split half will require the Teensy to be mounted upside down,
dead bug style. I will mount headers on TOP of the Teensy, and the TEENSY USB connector will touch the PCB. The USB will be in roughly the same Z position, but it will be flipped upside down. The downside to this is that it blocks the reset button, but I added extra buttons to get around that.
I will eventually redo the PCB to add an AT90 AVR instead of the Teensy. The only thing stopping me now is that the cost of the components on a Teensy++ make putting a prebuilt Teensy++ on the board the cheaper option!