Strange decision, as systemd-nspawn[1] specifically mentions and supports btrfs as a CoW filesystem for its containers. And as far as I understand, systemd is primarily developed by Red Hat employees. So either they'll add support for CoW alternatives, or they'll remove btrfs support from systemd-nspawn all together.
nspawn uses btrfs snapshotting natively for its templating and no other FS (ZFS was explicitly rejected by Mr. Poettering because "it's not in the kernel") so yeah either they are going to have to do something about this or there will be a significant step down in functionality for nspawn. I can't see how this isn't really bad news for nspawn.
I guess one option is to pull btrfs tree into Systemd :-)
[1]: https://www.freedesktop.org/software/systemd/man/systemd-nsp...