I think it would be neat to have a PVP/PVE type content where each of the 3 major cities have their own coliseum, players enter and are matched vs other players, with random monsters being released simultaneously.

For 6 days competitors from each city build up match wins, then on the 7th day there is a competition between the top X players between each of the cities.

This could be expounded on to have a seasonal event later as well.