I figured out an admittedly ugly workaround to the problem of not being able to boot from an SD image once the EMMC was running Manjaro 2.04. I was able to get the system to boot from a Manjaro 2.02 SD card image. From there I knew I could install gparted and blow away the partitions on the EMMC drive. After doing this I still had intermittent problems getting SD images to boot, but I was finally able to boot to the emmc installer image for the version of Manjaro that I wanted (XFCE 2.04, moving from KDE 2.04). This is, however, a less elegant solution than the one spikerguy pointed to above. If anything had gone wrong I was ready to crack open the case and pull the emmc chip and flash it using my pine64 emmc to usb adapter. Without that fallback I'm not sure I would have taken the risk.
So I'm sorted now, aside from so far not being able to get cups running to where I can pull it up from a browser. Overall I am really enjoying Manjaro with XFCE, and it is obvious how much work the Manjaro team has put into the ARM version of both desktop choices.
So I'm sorted now, aside from so far not being able to get cups running to where I can pull it up from a browser. Overall I am really enjoying Manjaro with XFCE, and it is obvious how much work the Manjaro team has put into the ARM version of both desktop choices.