If you're a button, you have one job: to transmit Morse code from the finger to the machine, Morse code representing a complicated POSIX shell command. And also to power down this entire one-button terminal with a 3 second press, power it up on any button press, with a firmware reset if powered up by a 30 second press.
Now I am imagining a typewriter with just two huge round buttons, next to each other horizontally, and a spacebar bellow them:
A press of each round button rotates the typing ball accordingly, pressing the space prints the chosen letter and resets the ball to the neutral state. This whole thing should probably be electric lest you'd have to press the space bar by smashing it with both fists.