This optional board takes the same size and plugs behind the display module. 

It makes wiring the daisy chain easier, and it can be populated with an ESP8266 master and/or a 170V and 3.3V power supply from a 9V input.

There is jumper on the back so that we can isolate the powers if several boards need to be populated with HV supply (in case we use a lot of nixies :-)

If no components are populated, the board simply acts as a wire. It could be considered a waist but making the wire is boring, and PCB manufacturing makes it for almost the price of cables and connectors... It also allows only HV caps to be filled and the power supply to be filtered locally.

HV DC

For the high voltage power supply, I copied a commonly used design from :

https://threeneurons.wordpress.com/nixie-power-supply/

It does not have a perfect efficiency but it is simple and cheap.

For 3.3V, the simplest and cheapest solution I have found is two linear regulators in series. A 5v and a 3.3V. This limits the input voltage to 9V.