[In-game implementation suggestion] arena system.
there could be an NPC in each city representing the gladiators, having their own reputation, their own store and a RANK based on the arena games that have already been played.
Reputation-related, there may be levels like in factions, allowing you to purchase increasingly better items focused on PVP, and having your own quests to raise your rank. These items and runes would also be extremely important and impactful at the end of the game, as they would impact on wars and domination.
I would particularly recommend 3v3 arenas that would be made between players of similar levels. EX: 25-40, 40-53, 53-60. There would be a RANKED system based on player wins and losses and a faction and coin-like reputation system for purchasing PVP-focused items like runes that could do extra real damage to players, extra defense against players, control resistance coming from players, etc. This would help players gain more PVP experience even though they don’t have LVL to be relevant in wars and RANK would encourage everyone to play.
So there is no inequality at the beginning ( like a player starting in the arenas will fall with someone who played the entire first day in the arena who is already FULL SET PVP [tryhards everywere] ), you can have specific times and days for arenas to take place, or a weekly limit on coins and reputation gained in the arenas.
Obviously, it would be very interesting to have a sort of coliseum somewhere on the map, representing where the arena takes place.