You can find a new version (0.1.1) on testing repo for s6-boot. This version will become the official version at 2016/06/23.
This version come with a lot of change, and need manual intervention. The runit-obarun package is now in conflicts with s6-boot.
First, you need to boot on other system like obarun USB stick.
Then arch-root the system.
Enable the testing repo in pacman.conf
Remove the file /usr/bin/poweroff, shutdown, reboot, init.
Install the new version of S6-boot and s6opts
Remove in /boot/syslinux/syslinux.cfg the entry init=/etc/s6/init if you have one
Be sure that the directory /etc/s6/boot-serv/uncaught-logs have the good permissions, it means s6log:log (normaly the package do it for you). If it's not the case, change it.
Be sure that the directory /etc/s6/boot-serv/service/s6-svscan-log/ contains a fifo file (normaly the package do it for you). If it's not the case create it like this : $ sudo mkfifo /etc/s6/boot-serv/service/s6-svscan-log/fifo.
Be sure that the symlink at /etc/s6/compiled/current point to /etc/s6/compiled/default
That's all
Exit from arch-chroot and reboot.
note: You need to rebuild your database for rc service and/or enable classic service like e.g. this :
$ pacman -Sy dhcpcd-s6serv dbus-s6serv
$ s6opts enable dhcpcd
$ s6opts enable dbus