Every medieval movie got its arena with arena teams, 1v1 and up to 5v5. This is the perfect opportunity to get some competition in this game! By being able to make and join arena teams you could unlock cooler looking weapons the better you get. If this is implemented there should be a ranking system, making lower ranked teams fight teams at their skill level, by doing this the arena part of the game stays balanced. A few arena-only maps would be awesome, as long as its not to big.
Every team should get their own Banner to customize. Selecting emblems they can place on the banner, maybe a border and a background colour. In my opinion, this would be a very attractive part for the more competitive player.