Similar to the duel mode in For Honor, wouldn't be cool to fight your way against other players to see who are going to be the greatest warriors of the Odyssey. It can be 1v1 or more, but in my opinion this mode is essential in AC Odyssey. What's even better is that AC Odyssey will most likely not include any multiplayer features, so this will eliminate any distraction that might affect the devs from working on too many features as it will give them the opportunity to focus on this specific mode to continuously make it more fun and variant as time goes by.
*Image source: https://www.pastemagazine.com/articles/2018/01/first-assassins-creed-origins-expansion-the-hidden.html