I personally dont care if its rust, python, C/C++ etc.... what I do are is that its breaking things on essential services. At work we tried and found a couple of install scripts stop working because of the sudo issue. And that got us off Ubuntu server and now on Debian server (containerized but still). Thank god for CI/CD or this would be an issue later on. I hope they get everything rock solid because you cant have core utils deviate all that much given how many services rely on them. Accuracy should be more important than speed.

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)

The utils are producing incorrect values.

The project is just new and under testing. It has nothing to do with the language it's written in.