Matt, firstly, thanks for all your work and totally sympathetic with how projects can be influenced by outside sources that eventually make them rather lost in the heady whirl of changes.
However I would like to sound a note of caution about the MCCI library for use with the Arduino’s based on the ATmega328P.
I’ve been answering many questions on this forum over the last six months about DIY Arduino Pro Mini + RFM95 (or similar) builds, I recently had to migrate away from the MCCI repro as not only was I originally using an older version that appeared more stable, but the Arduino compiler update in v1.8.10 ballooned the older code size so it would no longer fit in a 328P even before adding any actual sensor code. To support answering the maker community about getting a DIY device working, I published my work in progress, along with an account of how I arrived at the setup & my findings on its reliability: https://github.com/descartes/Arduino-LMIC-example
Whilst supporting someone getting a LoRaWAN tracker going, I realised that the combo I was using didn’t actually compile on Windows for what seemed like any reasonable version. So I spent a long weekend with a huge matrix of library, IDE & OS and finally arrived at your 1.5.0+arduino-3 working just fine AND compiling using the latest Arduino IDE AND on Windows as well as macOS.
So as a supporter of the concept of the affordable, starter, maker, DIY type device, right now I’d still be recommending your library - you are saying it’s not had much love of late and you are definitely not going to do any more work on it - but it doesn’t mean it has stopped working and for me for the last few months, I’ve seen others use it to good effect so it definitely currently has value.
I’ll redo the testing matrix in a slightly more scientific & publishable way so that people can make informed choices. A good percentage of issues is hardware (soldering!) related or just understanding the pin allocations. Another chunk is documentation of the event loop when people start adding in their own code. These are all variables outside of our control, so having a reliable library helps eliminate one big area of debugging a DIY device.
It is interesting reading about the evolution of the various offerings and how they have ended up where they are. I wonder if there has been too much evolution and if perhaps looking at some of the non-LMIC work, like Ideetron’s implementation, and having a group effort from a clean sheet would stand the smaller device creator in good stead. The LoRaWAN spec has some nicely delimited sections making it very suitable for such a project.
I am acutely aware that there are those that would have us run on “Big Iron” as the cost of the smaller ARM MCUs are of the same order as the ATmega & ATtiny 1-series parts, but the complexity of the ARM peripherals, the blizzard of supporting code just to do a Blink & having the Semtech code base as pretty much the only choice isn’t educational or maker friendly.
Now you have freed up some time & brain capacity, good luck with your future endeavours.