Poettering is building off other recent systemd additions to allow downloading the root disk image itself via HTTP and attaching it to a loopback device and making it mountable. Ultimately the effort will allow pointing the UEFI to a single URL where it can then load the Unified Kernel Image (UKI) from and in turn picking up the root file-system and booting it up.
The current use-case sought after by Poettering is to help in testing and making it easier for his physical device testing for quickly and easily booting new root file-system images over the network via HTTP whenever the system boots.
This work-in-progress pull request has the preliminary bits for allowing booting from the root file-system acquired via HTTP. Lennart is already looking at extending it to support NVMe-over-TCP and other features in the future.
Those wanting to learn more can read Lennart's comments via Mastodon .