You might want to consider designing a separate six digit display showing not only date but weather data. Day, Date, Month, Year -> Temperature (indoor/outdoor, Cº, Fº -> Rainfall (in/cm) -> Humidity -> Barometric Pressure (in/Hg, mm/Hg) -> Wind Direction -> Wind Speed (mph, kph) Wind Gust Max Wind Gust Speed (rolling peak detector), etc. That way you could still use the clock concepts of multiplexing the tubes like a normal Nixie Clock, and the Pinball Effect. None of the things I mentioned are that difficult to translate into OTF sensor instrumentation. You could even use the IN-19A/B special character Nixie tubes (or IN-15A/B).