Posix combatibility should be the goal, and breaking GNUisms isia good thing. BSD and GNU have always been slightly different. (Once upon a time I'd talk about sysV but that seems dead now). Either write posix or be clear that you dependion GNU - depending on something without being clear is a bad thing.

i don't think rust coreutils are posix compatible either, but that is the bugs they should be working on first (ane they are clear that they have a lot of such bugs so I can't blame them)