Will we get something like

rootAmbient(MyAmbient

) or maybe all instances of the ambient above the tree?

No plans for this. Why?

I imagine in nested navigation it would be useful to retrieve the root navigator in some scenarios.

Consider having each nesting level provide the list with an new action appended. You can wrap this functionality in a helper

Section(name = "Address") { ... }

that updates the navigation path by providing the list. It would be useful to use something like kotlinx-collection-immutable collections for this as they handle list structure sharing for you. Alternately a cons/cdr style linked list using immutable data classes would work as well.