Some sort of Gladiator Arena Mode would be Decent in this game. Look at the movie Gladiator for a bit of inspiration. 1v1 duels 2v2, 4v4, 10v10,practice mode etc.
Arenas with NPC crowds shouting maybe throwing the occasional cabbage in the arena etc. Spike traps etc to kick players into.Maybe a couple chariots or horses in the mix in certain Arenas.The option for 1v1 jousting could be decent also.
Have it so it keeps a record of your arena modewins and losses and shows your opponents records beside their name before a round starts. A record of your total kills and deaths also.Ranked and unranked matches.
I feel this style of mode that offers a few various styles of arena combat would be a good addition to this game and many would enjoy.