I managed to got the phone back on stock rom...
Here's what I did and found out so far:
The fastboot option - fastboot -c board_sapphire.disable_sdcard=0 DOES NOT work on three versions of RA-Recovery image 1.2.0, 1.2.1, 1.2.2.
However, it DOES work on RA-Recovery v1.3.2 and I do too managed to flash SPL to engineer 2005 from SD card. But when I attempt to flash the radio in recovery mode, it will just freeze at opening update package... so I downloaded SAPPIMG.NBH, reverted my phone back to factory ROM. Note: I've tried to flash sappimg.nbh before I flash engineering SPL 2005,
Even though the phone is now back on stock radio, SPL and ROM, the sdcard is still disabled! In fact it is even worse, because on stock SPL, and ROM, I can't root at all without sdcard access. Anyone know how to enable it?
Nexus 4, 5th replacement, settled.
Nexus 10, 5th replacement.