Command line option to set niceness

[Rhys Ulerich]

Would it be possible to add a command line option, say -n, to cause
parallel to spawn processes with a modified niceness?  Possibly
feeding -n with no option would be equivalent to prepending the
command with nice(1) and -n [#] would adjust the priority per
nice(1)'s page.

Admittedly, the user can simply use nice wherever desired.  My
interest is for having $PARALLEL or the configuration file pick this
up automagically.  That way I don't bring my UI to a grinding halt
whenever GNU parallel's doing it's thing.

Thanks,
Rhys