Comment # 3 on bug 948771 from Andrei Borzenkov

(In reply to Fabian Vogt from comment #2)
> To the "systemd-fstab-generator" messages: The "root=" parameter in
> /proc/cmdline is equvalent to an entry in /etc/fstab, so the warning is
> expected and necessary (although it could be worded better) as the mount
> options in /etc/fstab for / are ignored. See also
> http://lists.opensuse.org/opensuse-factory/2015-10/msg00138.html
> The goal is to remove "root=" from the default kernel commandline, but
> that's a multi-stage process. If the warning is too annoying or has any
> other side effects it'd definitely be possible to revert the patch or just
> remove the warning.
> 

It actually sounds like root= sysroot.mount should be placed in argv[2] by
systemd-fstab-generator. This way it will override any other unit and no
extraneous warning will be generated.

See http://www.freedesktop.org/wiki/Software/systemd/Generators/ for details.

Care to submit upstream pull request?