The ultimate holy grail of MMORPGs, making grind fun. There are various ways to do it. WoW has a slick battle system that somehow gives the impression skill matters (and perhaps it does). FFXI gave each party member specific roles and vastly different skills based on said roles, so coordination of those roles is what made the repetitive mob battles (sometimes) a little enjoyable. Add the selective linking and agrro, plus the subjob system and you actually had an overall bearable grinding experience.
Unfortunately FFXV's grinding is simply plain boring for now, so they're adding features to it in an attempt to make team based combat fun. The addition of jobs will perhaps bring back the excitement of FFXI combat, but in my opinion what really has to be edited is mob behavior and AI. Every mob should have a certain range of random actions possible, like attempting to escape, getting hate more easily from healers compared to other monsters of the same kind, etc. It's easy to do and would immediately make combat fun. They already showed they can really affect mob behavior, so this should be feasible. Of course it would take some time, but consider it a suggestion, if any rep is reading this.