Nick, LORA uses chirp spread spectrum, with a signal that is ~ 125 kHz wide (in 11 bps mode). If we have sufficient spectrum to accommodate this, then it might be worth considering.
Sorry Bob, I must have miss-read your original posting? as I did not realise that your proposal was for a backup command link as opposed to an APRS user port. Considering the wide coverage area, and the need for only a small number of backup-capable ground stations, would it be reasonable to increase the requirements of the backup ground station to that of a "big-gun" EME station?
If the RX chain of an FM receiver was non-linear before the last IF filter, I'd expect that radio to be terribly susceptible to intermodulation? (though after the RX RF has passed through the last IF filter, then yes, linearity does not matter for FM). When I get a chance, I'll have to do an experiment with an FM RX, an RF signal generator and an oscilloscope connected to the 455 kHz IF...
73 ZL2WRW Ross Whenmouth