mainline u-boot can read boot menu from extlinux.conf, and provides a menu to console or display (if support), which is more friendly to boot.scr and debian provides a tool: u-boot-menu to update extlinux.conf.   in order to use u-boot-menu in armbian, need to update kernel build scripts, need to follow debian's build rules. or make change to u-boot-menu to fit armbian's kernel.