systemd-nspawn was created to provide rapid testing of systemd, and it was (and, for now, still is) marked as an experimental utility that isn't for production purposes.
If you look at many of the early blog posts mentioning systemd and containers/VMs, you'll actually see my work and my company (Pantheon) mentioned more than Red Hat. In more recent posts, you'll see lots of CoreOS influence. Project Atomic isn't working with systemd in any direct, significant way; you won't see much coordination other than in some shared philosophy about a stateless base OS, and even that is more attributable to CoreOS's influence than Red Hat's.
I think the influence of Red Hat on systemd is overstated. Of the two perspectives: (1) Red Hat driving everything and (2) Lennart answering mostly to himself, the latter is way more accurate, for better or worse (depending on your opinion of him).