The Branched 2015-02-11 x86_64 nightly fails to boot with:

Failed  to switch root: Specified switch root path /sysroot does not seem to be an OS tree. os-release file is missing.

Indeed there is no /sysroot/etc/os-release . I believe this is caused by a change to fedora-release:

* Tue Feb 10 2015 Peter Robinson <pbrobinson> 22-0.11
...
- Move os-release to /usr/lib and symlink to etc (rhbz#1149568)

lorax share/runtime-cleanup.tmpl has this:

removefrom fedora-release --allbut /etc/os-release

I'd guess that doesn't work when /etc/os-release is a symlink to /usr/lib/os-release ?

This is an automatic Alpha blocker under the automatic blocker policy:

"Complete failure of any release-blocking TC/RC image to boot at all under any circumstance - "DOA" image (conditional failure is not an automatic blocker)"