> Similarly, if you use .ars, you're taking up that namespace from the perspective of your internal users. If at some point it turns out that there is some resource under that name that you want to access, you're going to have a hell of a time rebuilding your infrastructure to not use that name.

No, you're not, because an internal management network does not have a gateway out to the internet. The management VRF does not talk to the global routing table. There would be no way to access a public .ars website even if you did not take its namespace.