Well, there clearly is not room in the image for idbloader & friends
So it must rely on the uboot on emmc
So, when you flash the emmc, there is no more a uboot...anywhere
Personally, I would hack the image, then test by disabling emmc
As so
15Mblank + kali + 1M blank,, fdisk image,, dd mrfixit idbloader, uboot, ATF to image
Try boot with working then non-working emmc
Maybe boot.txt need editing (&recompile)
As I said,, it must not have been tested, so I have little confidence
OR, if you can't do it right, why bother
So it must rely on the uboot on emmc
So, when you flash the emmc, there is no more a uboot...anywhere
Personally, I would hack the image, then test by disabling emmc
As so
15Mblank + kali + 1M blank,, fdisk image,, dd mrfixit idbloader, uboot, ATF to image
Try boot with working then non-working emmc
Maybe boot.txt need editing (&recompile)
As I said,, it must not have been tested, so I have little confidence
OR, if you can't do it right, why bother