Just got my hands on one of these. Looking at the existing targets the Espressobinv7-emmc target probably includes most if not all of the same hardware (cpu, ram, switch) but the patch seems to indicate it still depends on micro-sd for booting
commit de3387654b5b65dcd9029d68c8c2fab29f6fef84 Author: Tomasz Maciej Nowak <firstname.lastname@example.org> Date: Sat May 11 19:37:35 2019 +0200 mvebu: add images for additional ESPRESSObin boards This commit adds support for different iterations of ESPRESSObin. The added variants are: ESPRESSObin with soldered eMMC, ESPRESSObin V7, compared to V5 some passive elements changed and ethernet ports labels positions have been reversed, ESPRESSObin V7 with soldered eMMC. Please refer to: 584d7c5 ("mvebu: new subtarget cortex A53") for instruction how to boot OpenWrt image placed on SD card. It is advised for owners of V5 and previous with bootloader based on U-Boot 2015.01, to upgrade the latest version available at: http://espressobin.net/tech-spec. Signed-off-by: Tomasz Maciej Nowak <email@example.com>
The ultra does not have a microsd card slot so booting from the emmc is mandatory. I'm tempted to just try writing the sd-card image using dd and see what happens.