Personally i think current Kalos main cast also lacks certain liveliness and emotional touch to make them truly outstanding with Misty often being capable to make atmosphere more spicy and enjoyable to follow(with group chemistry when she made apparances in Hoenn being more diverse and humorous). I feel she has more potential as character left with her dream of water master offering multiple directions for build up and sequel from current position. With Misty fiery, sarcastic and gurly sides of hers containing myriad of various interesting quirks and tough, compassionate attitude being highly interested in how she would function in main cast once more recalling on all past adventures she had with older friends like Ash. Work on developing close friendship with new companions and accompanying them for awhile in same direction she may have been going on road of coming closer toward fulfilment of her own dreams(that is if issue with gym and sisters unreliability ever gets resolved).
Using current experience and learning at gym which could served as stepping stone to her advantage when she eventually go on journey in case she decide to continue pursuing her dream of becoming top class water trainer. With follow of Wallace footsteos in entering prestigue tournaments to make name for yourself, trying to become E4 member or their apprentice being logical progression forward for her charter and way to be promoted for someone who wants to become water master.
While making interactions between Ash, Serena, Clemont etc more memorable and vivid to follow thanks to her flirty and spunky nature. Maybe im abit greedy but Misty is great character and i wouldn't hesitate in slightest to see her comeback for season or half a season after almost nearly a decade of no signs of her in person. Whiuch has poitential to bring benefit for character, main story, her voice actor and many pokemon fans.