OK, trying to figure it out myself.

• Installed a Debian image from the device's page and booted it once to check if it works and let it resize its root FS. It is necessary.

• Got a modified debootstrap from https://git.devuan.org/devuan/debootstrap

• Debootstrapped with ./debootstrap --foreign --arch=armhf daedalus dev1 http://192.168.1.254:9999/devuan daedalus into "dev1" directory (http://192.168.1.254:9999/devuan is my local apt-cache service address)

• Installed qemu-user-static and copied /usr/bin/qemu-arm-static into dev1/usr/bin/qemu-arm-static

• Chrooted with an emulation using chroot dev1 /usr/bin/qemu-arm-static /bin/bash

• In the chroot executed export DEBOOTSTRAP_DIR=/debootstrap; /debootstrap/debootstrap --second-stage

Voila (well, kind of). We should now copy contents our "dev1" directory to our SD card with Debian installed. Please note that in my scheme we should preserve /boot, /lib/modules (/usr/lib/modules) and /lib/firmware (/usr/lib/firmware) directories from the original Debian installation. Note that /lib/firmware and /lib/modules are symlinks; they should become real directories in Devuan.

So that's it. Just change first getty line in /etc/inittab to "1:2345:respawn:/sbin/agetty --noclear -8 ttyS0 115200,38400,9600 linux" and comment out all the others gettys. Boot the Pi, connect with a console cable and configure your fresh system.

Oh, W1 over GPIO doesn't work. There is no DTO for that. I would be very thankful if somebody explained how to make it working.
"reboot" command loses both wired and wireless network interfaces until a power cycle.