Apple can change the software at any point. My hunch is that on initial launch they knew a lot of people would be worried about bad use of these devices (and it's interesting that by far most of the chat on the web has been about how potentially dangerous these AirTags are).The fact that I can share to location of any iDevice (iPhone, iPad, Watch, AirPods, etc) with my wife but not the AirTags is really beyond me and completely ruins the usage case (finding our carkeys...)
Once the dust settles Apple can easily add in the software ability for Families to share them with Family linked AppleIDs.
Anyway, I'm going to give AirTags a chance and see how they work in everyday use.