Also perhaps worth mentioning Baserock (http://wiki.baserock.org) which can reproducibly build an OS from sources in git and deploy the resulting artifact to various popular targets, kvm, virtualbox, openstack etc.
This seems to be associated with GENIVI, Yocto and OpenEmbedded for automotive. If this can reproducibly build any Yocto-based OS, are there plans to upstream this capability to Yocto?