OpenWrt on some devices such as Turris Omnia writes the squashfs (mounted as RO root fs) in the "root" partition and then, immediately after, in the same partit

OpenWrt on some devices such as Turris Omnia writes the squashfs (mounted as RO root fs) in the "root" partition and then, immediately after, in the same partition, it writes a jffs2 (mounted as RW overlayfs). So it can be done.