The keyboard on this Powerbook is basically the only component that appears to be in good shape. Appears. I can't prove that until I figure out the matrix since attempting disassembly to check would destroy it.
The bottom plate of the keyboard is pressed on so each individual plastic mount would have to be removed to get it off. I'm not doing that unless I really have to.
The keyboard has two 1mm pitch ribbon cables coming out of it. One with fifteen conductors and one with thirteen. Information on the Internet about this setup has been pretty sparse, but from what I can tell it should be a simple matrix. That doesn't explain why two of the conductors are thicker (until the connection point), but I'm only going to worry about that if brute forcing the matrix doesn't work. To that end, I've acquired a pair of FPC breakout boards on eBay.
They're 26 pin, and the ribbons are only 16 wide, but they were cheap and more pins will be more versatile for reuse once I'm done figuring out the matrix. The plan is to design a custom board with the FPC connectors and a footprint for a Teensy (among other things) to fit into the case alongside the Pi. Hopefully this matrix gives up its secrets without too much difficulty.