About the proprietary nature on the amateur bands, this conversation's been had a lot over the years about various other popular proprietary modes or codecs and I don't see any restrictions that prevent the use of licensed chips/code. This might vary country to country?
Use of reverse engineered things on the other hand, yes there are obvious legal issues here but outside of the scope of our radio license.
I'd say either stick to something that uses the official licensed technology or code and take advantage of the cheap chips, or come up with something (better?) that does not. I'm not sure a hybrid approach would be workable for anything officially sanctioned.
I did run some brief LoRa tests on the wide band transponder last year using the official chip in to a transverter and an SDR + GNU Radio for the decodes. I didn't progress this beyond receiving my sent messages or the next step using an proper chip to decode as other than for curiosity I didn't see any purpose to using LoRa here.
I've found https://github.com/rpp0/gr-lora to work better in practice than the one linked which I struggled with.
I contacted one of the chip suppliers in the past as noted they had a 14x MHz option printed on the board for testing in our 146MHz wideband frequency allocation here but they had not actually made any. They suggested a large order would enable their production or alternatively for test purposes just use the existing 433 one where they should work for test purposes but with bad performance. Never got around to testing if what they said was correct but it might mean the 869MHz ones may work to a limited extent a good bit off frequency.
Happy to run any tests if anyone wishes to.