Products can be uniquely identified by their SKUs, which have meaning to a business, but for categories there is no such business attribute in Magento; categories can only be identified by their integer ID, which has no business meaning. In Magento 1, this poses issues when attempting to integrate Magento categories with other platforms, for example Akeneo, because there is no way of relating the Magento category with the category in the other platform.
From what I can see, this is still the case in Magento 2.
So, I guess my question is this: Given a third party system which maintains category data in a format something like [code, name, parent_code, ...], how can we use the Magento 2 API to create and later update and delete categories using the provided code as a unique identifier?
If this isn't possible, then I think it needs to be. Most medium to large retailers have business identifiers for customers, categories, orders and many other things, not just products.