Personally was looking into the project and it was the first thing I searched. Wanted to jump in to say ive been using the Matrix protocol for 4 years and it has served me really well. I am less familiar w/ the LoraWan protocol or mesh networking in general, but I thought i would mention that the Matrix protocol has a reverse proxy service called pantalaimon that is meant to handle E2EE for 3rd party services. This may actually handle alot of your work load as far as encryption goes, but im not sure how optimized would be for the low bandwidth+forward error correction restrictions of the Lora protocol.