Could you provide the source code? It's a fork of Santa's Nixie Tubes, I'm wondering what the differences are and how I can maybe contribute to making it ready for 2.0.

The source code is all in the zip file on the downloads page. Take a look and if you are interested in contributing, I can throw it up on Github.
I added several optimizations to the original in order to speed it up and fixed some bugs. Things like configurable sleep between updates. I think it could be better still, and at some point I've wanted to completely redo how nixies are tracked, but I've been off Factorio for a bit and haven't had the time.

Thank you for your response! I love the mod and the effort you put into it. The Factorio 2.0 update has been amazing. I've had a look and I'm debating whether I should try to get this mod working as-is, or as you suggested maybe just redo it cleaner.

Are you at all interested in picking up developing an update for 2.0, or should we consider this mod abandoned for now? What ideas did you have with regards to how nixies could be tracked?

Yeah. I've been planning on a 2.0+SA run, but trying to put it off till I wrap up a big work project. I could probably take a look at what it would take to get this running. If they haven't drastically changed the API, it might just mean updating the version number in the info file.
As far as improvements, it mostly has to do with changing how nixies are stored, so there are less things that need iterating over.
I'll try to load 2.0 up this weekend and see if it's an easy update to get this working.

I've gotten quite far in getting the mod to work. The game now loads, which is a pretty big step. Please let me know if you want to collaborate and if so, how you would like to communicate going forward.

Edit: I have it working, but it still needs improvement with regards to the new Circuit Connection UI.

https://github.com/pindab0ter/UPSFriendlyNixieTubeDisplay

https://forums.factorio.com/viewtopic.php?f=25&t=119302

I'll be around Sunday afternoon, Pacific time and can chat more. Hangouts, SMS, Signal, Whatsapp, Discord?

Feel free to find me on Discord with the same username.

Request sent on Discord

Is your version working for you? I grabbed your version and it loads, but does not seem to work.

Mostly, but it's still a work in progress.