On the subject of building keyboards. I happened to remember an IEEE Spectrum article about building a keyboard into a typewriter by the way of shifter registers. Why exactly did they choose to use shift registers instead of a standard keyboard matrix? Indeed, it is simpler and uses less circuitry to use a conventional keyboard matrix. The shift register design was purely for making the custom construction and fitting into a myriad of different typewriter designs easier. The shift registers mean that the microcontroller board can be external to the typewriter, and only a few wires need to be run to connect them together. This is important because many typewriters may not have much space to put the microcontroller board within. Also, another benenfit of the shift register design is that it forms somewhat of a repeating pattern on the circuit board internal to the typewriter, so the board can be cut to any length without repercussions. Also, interestingly enough, they choose to use the Atmel ATmega68 microcontroller for the project too, the same microcontroller that is used in the Arduino board.
Lo and behold, this is an oldie but goodie: the IEEE Spectrum article is from 2011.
20181216/DuckDuckGo ieee spectrum keyboard shift register
20181216/http://spectrum.ieee.org/geek-life/hands-on/a-typewriter-is-a-terrible-thing-to-waste
So, here are more technical details on how the shift register circuit works. The CPU continuously shifts a 1 bit down the input of the shift register. When a key is pressed, it channels a cell to register as a 0 bit instead. The CPU can then read out the bit pattern and decode this to determine which keys were pressed.