Well, after over 70 views and no replies over almost 2 weeks, I finally got my unit working again. I bought the CSR USB to SPI adapter from Digikey and flashed the firmware posted here:
[url]https://forum.sierrawireless.com/t/bc127-do-not-respond-to-uart-and-connect-for-firmware-update/9516/1]
After the firmware flashed and all the defaults were reset, I got UART back. However, my project code was not ready for the protocol difference between Melody 5 and Melody 6, so I tried downgrading back to Melody 5 RC14 (despide reading that a backwards move from 6 to 5 was not allowed) but it worked! With 5 RC14 back on the device, my project worked once again.
But seriously… A proprietary SPI interface requiring a $15 adapter? Seems pretty sketch.
I dont know why the USB host mode didnt work. Perhaps a driver issue? Who knows.