It would be trivial to fork parallel. If people cared enough, a fork would appear and be adopted. That's the beauty of free software. If you don't like it you can change it.
It was already forked in its early perl days, and thus it's very hard to use it properly as build tool, as the non-GNU version has an entirely different argument syntax. eg on macOS or BSD. You really have to probe for the GNU version (the more popular and newer one, with this awkward citation and begging),
but for longer tasks it speeds up processing immensely. There's no need for Hadoop when you can use parallel. I'm processing hundreds of log files in one of my build-steps (similar to pgo, profile guided optimization), and with parallel it needs 30s, without 3min. This makes a difference.
My configure.ac recipe for the proper parallel is this, setting logs_all to the GNU parallel version.
dnl GNU parallel, skip the old non-perl version from moreutils so far
AC_CHECK_PROGS([PARALLEL], [parallel])
logs_all=logs-all-serial.sh.in
if test -n "$PARALLEL"; then
AC_MSG_CHECKING([PARALLEL version])
parallel_version=`$PARALLEL --version 2>&1 | head -n1 | cut -c14-`
case "$parallel_version" in
[0-9]*) AC_MSG_RESULT([$parallel_version])
logs_all=logs-all-parallel.sh.in
;;
*invalid*)
PARALLEL=
parallel_version="skip old moreutils version, need GNU parallel"
esac
AC_MSG_RESULT([$parallel_version])
fi
AM_CONDITIONAL([HAVE_PARALLEL], [test -n "$PARALLEL"])
Not really independent. Ole Tange tried to get his 2nd parallel into findutils (to replace xargs and allow parallel processing) in 2005.
Because it was written in Perl, findutils refused to add it. So Ole Tange contacted moreutils in 2009, but they never answered, but later one guy of them, Tollef Fog Heen, rewrote parallel in C, with just minor API discrepancies. They say it predates GNU parallel, because the 2005-2007 package was not a GNU project then. It was added to savannah as individual GNU project in 2010, Ole gave up inclusion into findutils then.
Hence I called it a "fork". Independent, yes, but when you know about the project, steal its name and put it into wide distribution under that same name, because you think your name has a better chance of being adopted, this is called a fork. Like a pitchfork. Poking into the original authors eyes with a sharp instrument.