As they wrote "We explicitly do not support really old kernels with really
new systemd. So far we had the focus to support up to 2y old kernels
(which means 3.4 right now), but even that should be taken with a grain
of salt, as we already made clear that soon after kdbus is merged into
the kernel we'll probably make a hard requirement on it from the systemd
side. " .. I think it will not be a "allow" … simple systemd requires kdbus and kdbus will be merged in the kernel … after the 2 years you have most distributions which use up to date kernels … which means Linux goes mainstream as RedHat defines it.

I am not against progress but if I look at the things now, I think I also could stay with a proprietary OS like Mac OS X because in booth worlds (I mean here only systemd) I have nothing to decide and no libre.

A little paranoia .. we know that the official kernel from Linus Torvalds contains binary blobs because of progress and to support as many hardware as possible. What is now if a essential component … for let´s say kdbus will be released as binary blob ? Then you have to decide to go RedHat´s way or use the linux libre kernel http://www.fsfla.org/ikiwiki/selibre/linux-libre/ and become a outsider.

As conclusion I personally find it very important to have # # (Linux From Scratch) and the idea of a # fork.