[snvzz]

To add to that (edit no longer possible): Selecting boot from SD card via the boot DIP switches is already possible.

This ROM won't even initialize RAM. All it does is fetch next stage from SPI, eMMC, SD or UART (xmodem), into SRAM (CPU cache used as RAM) and jump to it.

What's not possible is USB, as the (non-updatable) early boot code ROM within the SoC is trivial and obviously has no USB support.

Thus UEFI or u-boot are needed for USB or NVME boot.