Long story short, Lennart is trying to tackle how Linux distributions and software systems themselves are assembled to improve security, deal with the challenges of upstream software vendors integrating into many different distributions, and "the classic Linux distribution scheme is frequently not what end users want."
Lennart and his fellow systemd core developers have been devising a new way to tackle these challenges to come up with an efficient way to allow vendors to package their software for end-users, allow end-users/administrators to install packages regardless of the distribution at play, a unified solution to cover everything, and for software images to be trustable.
While others have tried tackling this lofty goal, Lennart and the systemd crew are trying to make use of Btrfs and Linux file-system name-spacing to overcome some of these challenges. In particular, Btrfs sub-volumes would be heavily utilized for different users, applications, etc. This would be implemented as a unified scheme for installing/updating OS images/apps/runtimes/frameworks, everything should be cryptographically verifiable, everything is to be double-buffered, and much more.
The systemd crew is already slowly working on this agenda and you can learn a heck of a lot more details by reading Lennart's blog post in full as it's quite lengthy with a lot of interesting stuff covered.