Yep. I tried the SMC trick too. I'm thinking the PRAM was holding onto the initialization info and it got wiped. I think the boot volume gets locked once the install starts, so it needs to get that info from the PRAM (NVRAM). It got zapped and now it doesn't know what to do.
... if the Firmware is bricked, I wonder if I can get it to boot with an external Linux system, like Ubuntu, then designate my external MacOS as start-disk? Wouldn't a standalone Linux have its own Firmware and Kernels?