If you have a plate, you don't need a PCB. You can use a Teensy 2.0 as a controller and wire up the columns and rows by hand with diodes no problem. The key functions can all be done in the firmware on the Teensy, no wiring changes are needed once you have the basic grid wired up.
Definitely going to be making a plate for this.
How powerful is a teensy? I was looking at the teensy a couple of weeks ago for another project, but the limitations on it are annoying. Then again, I'm not totally sure how this whole column thing works with keyboards, as I'm pure computer science, no electrical engineering background. Also, since I'm taking the effort to build a custom keyboard, I was hoping to add a bunch of features - USB hub, RGB LEDs, internal storage, SD card slot, possibly even mic and low power speaker or at least a sound chip for audio feedback. My hardware goal is to get to a spot that I can basically have an array of booleans (pressed/not pressed) representing all 72 keys which the firmware would be checking 500-1000 times per second. I could then write all the software around that to do the features I want, converting this array into what keys to send to the OS. (also, I'm checking info on writing self-installing drivers so that I could do some heavier AHK style stuff, but I need that key reading first)
I'm looking at other projects (
http://geekhack.org/index.php?topic=6292.0) from more knowledgeable people. I'm also looking at somewhat unrelated projects (
http://geekhack.org/index.php?topic=19458.0), that sort of "intercept" reprogramming dongle was the idea that originally lead me to the teensy.
It's rather annoying how difficult all this hardware side stuff can be. All of my usual work is with pure software, which is so much easier to make malleable. All my past similar projects (namely FIRST and other robotics competitions) I would only have to worry about how to program the inputs, never how to get them.
To be clear, the entire keyboard will be blanks except for the interrobang esc. (ideally, all thick black/dark grey PBT, with the interrobang being doubleshot orange on black). Every single key would be programmable.