I get that it's meant but be wrapper for common use cases, but I use ZFS on root and had to craft a custom initfs. The other nice-ities sound great (some BTRFS inspiration?), but some of these are at distro-devel level.
I looked into doing root on ZFS, but I ended up settling for /home on ZFS. Maybe I'll revisit it next time I build a new system when I'm more comfortable with ZFS.