apparently the /usr/lib/udev/rules.d/64-btrfs.rules files cause trouble. I never used btrfs, so it's really difficult for me to help you about it, maybe you can open an issue here:
https://github.com/gentoo/eudev/issues and asks for help or correct instructions to use btrfs. Also, you can try to remove this rules ( i don't understand correctly what it do).
about the dbus trouble :
you should have the solution on the referred post that you told about.
I give you again the procedure to follow :
change the /etc/pam.d/system-login
enable as root consolekit daemon (not really necessary if you use ck-launch-session in your .xinitrc)
create the user (if it's not made already)
run (as user) the command : s6opts user
enable dbus ( as user too) : s6opts enable dbus
log out , reboot, log in
tell me if it's not working