While it is not necessary to construct a working data set without node ids, the API needs it to offer operations to modify the hierarchy. Inserting a node needs a 'parent' (to create a lower level) or 'predecessor' (to insert at the same level), and the only unambiguous way to identify a node is by id (a resource may be referenced multiple times in a hierarchy).
Thus we should require a node id with v1.0.
While it is not necessary to construct a working data set without node ids, the API needs it to offer operations to modify the hierarchy. Inserting a node needs a 'parent' (to create a lower level) or 'predecessor' (to insert at the same level), and the only unambiguous way to identify a node is by id (a resource may be referenced multiple times in a hierarchy). Thus we should require a node id with v1.0.