However , There no point of bring Misty back if she doesn't have her sarcastic, silly and Sassy side of her.
Plus, Other character need to do thing that open up her angry and sarcastic type .
Plus , If Misty treat Clemont as formally as Serena then it won't make any difference.
I want Misty to point out how Clemont's invention usually blow up and if any of his invention tries does something weird of perverted to her then I want Misty to smash that machine on Clemont's head.
After all , Misty is brutally honest and capable of saying thing others can't tell .
Currently The XY series is Boring because of Formal & Boring relationship among the main group.
By the way , Does anyone notice that Ash look empty now ?
I mean Whenever I see Original Ash , I can actually feel his emotion ! He feel so real.
But current Ash , I don't feel anything ! He look like a empty doll with nothing inside of him.
Original Ash feel like an actual Boy while Current Ash feel like a model that our parent wants us to be.
To be fair; character interactions arent only point and reason which would give purpose behind Misty return. There is also opportunity in bringing more unpredictability and varety to pokemon series with her own dreams, storylines and unresolved conflicts. Followed with restoring on bonds she had with Ash generating new interactions and connection to past. Giving us update, increasing continuity and making storyline more connected and plot driven.
Not to mention help increase ratings and popularity as well with many wanting to see Misty back.
As for her sarcastic, quirky, temperament nature. Misty always had that being one of recognizable parts about her personality. Whether we are talking about early days like Kanto, Johto or later in Chronicles and Hoenn(depending on episodes and characters she interacted with).
Diference compared to early days was that Misty would express sarcasm, flare and disapproval in non violent way like using logs and punching people left and right. Rather resorting to playful teasing, acting abit arrogant at times or just yelling and holding grudge against someone when provoked or insulted her.
And i have no problems with this going well in accordance to maturity and character developmernt Misty experienced., Becoming stronger, more independent character. Became closer friend to Ash and Brock and evolved as person herself through journey feeling like she gained something from it.
So while i could see Misty being sassy, tease or be skeptic and frowned over Clemont inventions(especially if they explode in her face). Ash clueless nature and acknowledgemernt of Serena having crush stirring things up causing certain amount of friction or jealousy. Or Bonnie potential proposal that Misty marry her brother making her irritated and embarassed.
I don't think she would go over the top in starting to hit others and be super rude or aggresive(especially to characters who did nothing harmful or wrong to her). Simply being out of character and going against any growth she went through.
Because to have humor, arguing, drama or playful interactions Misty is perfectly capable of delivering that among Kalos cast without being violent.
As for Ash like i said before.
Its needed to take in account how relationship and chemistry between friends largely depends on their personalities, quirks, backstories and circumstances.
With someone like Misty for example Ash has entirely different friendship. Based on mutual teasing, enjoying in competing between themselves , get into clash challenging each other ideas or express admiration and close bond full of care and support through play . Thats why infront of her we usually see more of that stubborn, impulsive side of Ash come on surface(which was evident in Hoenn as well in Mastermind special and release of Togepi).
With Dawn we saw more energy and jokes going between Ash and this character, Due to having almost sibling type of relationship. With friendship being based on mutual support and understanding.
With current companions roles are reversed with Ash being one who is wisest, most experienced and knowledgeable member of main group. Serena, Bonnie and Clemont look up to him not going in clash with his decisions, deliver any critic or much teasing. Hence why Ash has no need to act sarcastic or brash at all.
Being required two way alley to produce organic, unforced and endearing dynamic between characters.
Hence being reason why Ash may be less joking and bratty than he used to be even as more mature character. Because surrounding and who you interact with largely influence your characterization determining what kind of chemistry there will come out of it.