View IO & ESD solutions supporting GPIO, I2C,RGMII, SD, LVDS, HDMI & analog/RF across multiple technology nodes full description to ...

Each Nixie is controlled by a K155D driver chip, with the driver chip controlled by an I2C IO expander. The keypad is where this gets interesting; electronics are one thing, but electromechanicals ...

Our guess it that an SPI / I2C IO extender could lift this limitation. A quick (shaky) video is embedded after the break.