I'm also wondering whether the GNU system should recommend using zstd
instead of or in addition to xz for compression purposes.
I'm not sure GNU explicitly recommends anything. Although the tarball
examples in standards.texi and maintain.texi all use gz, I don't think
even gz is explicitly recommended. (Which seems ok to me.)
Personally, I would support lz4 over zstd simply because more GNU
packages already use lz4.(*) Both lz4 and zstd are quite a bit less
resource-hungry than xz, especially for compression. I don't know if
there is a technical reason to prefer zstd.
In general, I think it can continue to be left up to individual
maintainers, vs. making any decrees. Automake supports them all
(among others). --best, karl.
(*) Looking at a listing of ftp.gnu.org, I see only gmp using zst, and
perhaps a dozen or so packages using lz. Basically always in addition to
another format.
