My 2 cents…
Add a system that allows boss farming specifically. This could be achieved by quest chain accomplishments (i.e. one must complete the quest and sub quest attached to it in order to unlock) and flags, that such act as a must done (such as Must defeat X boss in order to unlock for this repeatable system.
Ideally (imho) one must:
- [li]Complete Normal mode[][]Must complete Quest and sub quest objectives to unlock[*]can only participate up to the bosses they have previously encountered in current Campaign Mode
Could be something along lines in the below video on Edge of Reality
WolfOverclockedGames where you run a gauntlet and face off against the bosses
or
Once pre requirements completed unlock a special Rift (new zone) also on edge of (or altered) reality that has locked and unlocked way-points/rifts/doorways scattered around the zone. One for each Boss (and again if your in say Elite but have only killed one boss) that that has been defeated (as unlocked).
Either ideal (imho) should yield zero xp, after all this concept is about getting gear and reducing time served in its pursuit.