Okay! I think we can set as main the element with the class xcontent on these view page. I’ll need to check what this class is used for in other pages, but it seems like what you described.
For the edit and create buttons, they could technically have a navigation role (they contain links), however I think complementary is more suited for them. This choice is also motivated by the already high amount of nav landmarks we have in the layout.
Those buttons are not part of the content, but for the most part they are linked to actions that are based on the content. They cannot work independantly from the content.
I created an issue on jira, and I’ll start working on it soon if there’s no assignee by then:
https://jira.xwiki.org/browse/XWIKI-20696