One of the constraints we’re dealing with is an entrenched assumption that any boundary=administrative boundary needs to fit into a single, overly simplistic admin_level=* hierarchy. That leads to fraught questions too, like whether a federally recognized reservation’s boundary should be admin_level=2 or 3 or 4, whether it’s a good idea to have crisscrossing chapter boundaries and county boundaries with the same admin_level=*, and at the end of the day that still doesn’t solve the problem of how to indicate that the chapter belongs to the reservation rather than the state.
border_type=* can resolve some of the ambiguity for mappers looking closely at the data, but not for the constellation of existing data consumers that will go on treating native boundaries like their nonnative counterparts. However important the symbolism around the boundary=* tag we use, there’s a certain danger in erasing distinctions too. I think we’d have to coordinate with data consumers to avoid unintended consequences.
For what it’s worth, the Polish community has long mapped Catholic administrative territories, which are parallel to the secular hierarchy, as boundary=religious_administration with admin_level=*. So maybe these agency and chapter boundaries can have admin_level=* without issue. If we need to emphasize the administrative nature of these boundaries, what if we migrate to a new boundary=indigenous_administration tag? Yes, it still includes the word “indigenous”, but depending on how it’s documented, maybe the tag could be positioned as acknowledging rather than marginalizing indigenous groups?