Next time I'm designing a keyboard I think I will look into programming the AVR from scratch myself (and how to solder the sucker in there in the first place...). This would also allow me to use a less powerful AVR if I would want to, or more powerful of course =) And the chips are truly surface mounted, and [SIZE=0]tiny![/SIZE], it would fit anywhere...
Using a couple of multiplexers/demultiplexers the number of needed pins drops significantly too. I found that the HHKB has a smart solution. It uses a binary-to-decimal decoder chip for the supplying the rows. It has 4 input pins (4 output pins required from the controller) to take a 4-bit binary number. Depending on this binary number it lights up 1 out of 10 output pins supplying 10 rows, they are then interleaved to give 5 actual rows on the PCB layout. An 8 to one channel demultiplexer for the columns would requires 4 more controller pins (1 as the input to the controller and 3 for selecting column). So in total 8 controller pins for a total of 8×10 key positions.
I don't know if the Teensy even fits Between a plate and the PCB. If it does it would be possible to put it under the space bar. This would require the Filco style stabilizers, since the stabilizer wire will get in the way with a cheery one. And Filco style requires a mounting plate.
I would really recommend getting two-sided PCBs with solder masks and everything. With the all the cheapest choices they aren't almost any more expensive at pcbwing than what DOX paid for his (and there probably are other places in the same price segment). Shipping might be more from China though I guess.
Edit: Also I managed to hook the Teensy into my PCB on that square matrix layout prototype, using only 30 or so jumpers. The routing do require some hair pulling and teeth gnashing though =P
