So, life has been busy and I've not yet had a chance to work on this further.
But, I've shared what I've done so far over on GitHub in case anyone wants to try it: https://github.com/heliomass/Threads-Federation-Tracker
It's really just a proof of concept right now, just a bash script.
The whole thing needs to be rewritten in Python so I can add features, starting with a local DB to track changes and trends.
I'll get to it in the next few weeks, but if you do decide to give it a try as-is let me know how it goes!