Answering self,

using the gentoo template as base:

-- MIRROR=${MIRROR:-http://http.debian.net/debian}
++ MIRROR=${MIRROR:-http://auto.mirror.devuan.org/merged/}

-- configure_debian_systemd $path $rootfs
++ #configure_debian_systemd $path $rootfs

lxc-create -n lxcdev -f /path/to/your/lxc.conf -t
/usr/share/lxc/templates/lxc-devuan
lxc-start -n lxcdev

myuser@lxcdev:~$ ps -ef|head -2
UID        PID  PPID  C STIME TTY          TIME CMD
root         1     0  0 14:12 ?        00:00:00 /sbin/init

Uses about 378M, 135 packages installed.

However, i see these in top:
root        20     1  0 14:12 ?        00:00:00 /lib/systemd/systemd-udevd
root       128     1  0 14:21 ?        00:00:00 /lib/systemd/systemd-journald

So it's a work in progress.

Cheers,
Nuno