Not having heard of parallel, a few years ago, I wrote a script which started out as 'el' (Edit Lines) in Python.
El would need a better usage message to be useful to others. To support parallelization with el, I'd probably add a dependency on joblib (which dask-distributed and dask-ssh also support).
Anyways, a few features that may be worth adding to parallel:
## ENH: -0 option for null-terminated input
We tend to assume that all newlines in output are escaped; which isn't the case with all tools. FWIU, GNU find *does* escape newlines in filenames:
touch 'file'$'\n''name'
find . | xargs echo
find . -print0 | xargs -0 echo
## ENH: -v for verbose to print input to stdout or stderr
For debugging, printing the input line to stdout or stderr first can be really helpful.