I think some way to increase player engagement is to have cross server play and duel fight or match.
It would be classic and stylish, and fun too, to have players challenging other players in a duel of champion, 1 on 1.
It will increase the game intensity. And fair chance to newbie player to challenge senior player. So it would take real talent and cunning skill to win the duel.
Fair play system and rules need to be created. Punish abuse by senior player to junior player. And rewaed junior olayer winning duel match againts senior player.
Measure by strength and other stat to ensure balance. This might be one of the mini game players will enjoy.
Larger cross server play also need to be developed.
I know that you guys want to stick to the original programming script. But it should be easy to add new game feature that will elevate your games to legendary level.