Comment # 1 on bug 1180236 from Takashi Iwai

The firmware supports only XZ compression, and openSUSE stable/master branch
already enabled the ZSTD initrd support.  The rest is rather the change in
dracut.

The kernel compression itself has been kept in GZ for simplicity.

The module compression is done in another way than the kernel config, and it's
very unlikely we switch to zstd for now, as it needs to touch quite many other
places (obs-pesign, rpm-config, dracut and suse-module-tools, as well as other
user-space stuff like yast2-sound and such checking the module files).

So, at most, a possible low-hanging fruit is the kernel compression itself, but
I'm not sure whether it's 100% safe or it's worth.