Oh, thank you so much for that! So, I have good news and bad news… the bad news is that I was apparently a bit hasty in removing the plugin when I saw it was no longer supported. D'oh.
The good news is that its config file remains, just not in the plugins/ subdirectory where I was looking for it. It's in the Calibre configuration directory, filename: device_drivers_KOBOTOUCHEXTENDED.py.json
Thanks again!