raspbian repos incompatible with rpi3
In the devuan_jessie_1.0.0-beta2_arm64_raspi3.img.xz image, /etc/apt/sources.list lists the raspbian repo for firmware. However, raspbian doesn't seem to currently have an arm64 port. This leads to an error message to that effect when doing apt-get update. I can think of a couple of solutions here:
Remove the raspbian repo altogether from sources.list until raspbian has an arm64 port available.
run dpkg --add-architecture armhf, and change the deb line for raspbian in sources.list to dev:armhf.