Regarding interview you guys are mentioning and statement of Misty continuing to make cameo appearances in future, i believe this is what your looking for:
From interview with Masamitsu Hidaka(worked as director for pokemon series up to Battle Frontier, afterwards stepped out and continued to work as storyboard artist) on Pokebeach from 2008:
What about the main cast on the show? Since he had talked about how they like to “switch them up,” I explained to him that many fans want Ash, Misty, and Brock reunited again together. But, he reaffirmed what he said in the previous interview and said it wasn’t going to happen. I asked him what he meant in the previous interview about Pokemon Contests, and he said he just meant that characters like May have come back for a few episodes in Pokemon Contests, so Misty could come back too. He said, however, that Contests don’t appear to be her thing, so if she were to come back, it would probably be to join Ash in a battle or to just meet them somewhere.
Followed with his previous response:
If she is to ever return to the show, it will only be in a minor role as something like as a rival for a tournament, similar to May returning for a few Diamond and Pearl episodes.
In other words he noted as possibility that Misty has in flesh appearance again like May did coming either for tournament, to join Ash in battle or just meet him and companions somewhere on road. But that was stated back in 2008 and now 6 years later nothing came out iof it.
Bear in mind though how mr. Hidaka by time he gave interview was no longer in contact with writers like he used to be due to not being involved in big decisions as storyboard artist anymore. Thus not being familiar with their plans nor upcoming decisions compared to past. Fact how he didn't even knew about pokemon Platinum coming out around that time not knowing how to respond to fan inquiry, while everyone on online pokesites were already long familiarized with it only further reinforces this conjecture.
Leading to reasonable conclusion how things mr. Hidaka mentioned in interview shouldn't be taken as 100% true. Which can work both in Misty favor(in light of despite what he said Misty still having chance that writers change their mind and bring her for at least semi permanent role again like it was case with Charizard).
But this can also work against Misty unfortunately with his words not guaranteeing that Misty will even receive appearance for few episodes.
Otherwise how to explain writers ignoring to use her for past 8 years?
Its not like writers didn't had several opportunities, very plausible ones to bring Misty back at very least for few episodes to enrich on show atmosphere through her vibrant, enjoyable personality making people happy, provide update, gain more growth and help influence one of show plots which were running at that time.
Coming to catch rare and new water pokemon learning new things(like they did with Clair in Unova)was one of ways to bring Misty back in Sinnoh or Unova,. There is whole World tournament from BW2 games which was one of best and most prominennt ways to reintroduce Misty again since she could both help advertize it due to being present in new games, was more than qualified to enter as gym leader and trainer. Along with this being perfect way to push her story forward since entering tournaments with strong competition and making name for yourself is one of things crucial in order to become high class water expert, water pokemon master.
In as much giving her opportunity to battle trainers of higher calliber, meet champions and specialist she would never had chance to see before and sharp skills through intense battles greatly advancing her water master dream. Providing more experience and challenge than its case at gym rotting currently with her story and dreams going nowhere, aka stagnation.
They could have Misty play role with Dawn getting Togekiss since she posessed Togepi, Togetic having most knowledge in its raising than any other main character. Have her appear when Ash returned at Pallet two times in a row(after DP and now after BW), but once again writers completely left her out.
I cannot even stress out enough how in new XY series there exists several very valid reasons to bring Misty back. At least for arc or something. There is fact of Kalos introducing E4 member of water types Siebald from who Misty could learn a lot about bonding with water pokemon on closer level increasing her skills and how to overcome their weakness. E4 are best mono trainers in world, Misty dream is to become best water trainer in world idolizing Lorelei wanting to become strong like her. Since E4 are labeled as type masters in game and Misty wants to become water master its not hard to find connection and why she would be extatic to meet him.
There is fact of Misty posessing Gyarados which can mega evolve giving her marketing value to both help promote games and be involved in relevant plot which in Kalos revolves around mega evolutions and Team Flare which wants to control therm for wrong purposes. Making massive step forward in her knowledge as water trainer by achieving close level of understanding unlocking its true, full strength play. Which once again is expected from someone who strives to become master.
She can return for water based tournament like Whirl Cup was showcasing her new skills and how much she improved, advance her dreams, test out her strength possibly against Ash like in good old days reviving that competitive fire and rivalry between them which was always present in wanting to prove each other to be better. Along with capturing new pokemon and guess what promoting fairy type through Azurill line.
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Its still hard to believe that Misty's last in flesh return was in 2005(2006 if you count Mastermind special, but im referring to regular main anime). And writers left her out for each and every opportunity like she is nobody and never existed.
Thats definitely sad and discouraging, to think that once such important character who is original female heroine for pokemon series, part of most iconic and recognizable cast in world(original trio) which paved way for future generations to come and allowed that pokemon anime becomes hit, incredibly popular worldwide is discarded and abandoned like last trash. Like Misty never existed or played important role in pokemon series, like she never left any influence on Ash, other characters and pokemon storyline.
Like she doesn't have her own dreams, goals of becoming master of water types, live up to idol Lorelei, learn and catch as many water pokenon she can realizing how to bring their true strength on surface becoming like one when battling together, insecurities and flaws which deserve to be explored and tied up instead of leaving everything so abruptly cut and unfinished like all that hard work, learning on mistakes and growth was for nothing never leading her nowhere.
Bugphobia, parents which abandoned her and sisters, unsolved disputes with sisters or lack of resolution in what way and how she can come closer toward her ultimate aims with whole future and what she intends to do with her life etc. come to mind on first hand.
Like she doesn't have many people which like this character and support wanting that at least from time to time her existence is acknowledged, her story and progress receive update taking her somewhere, to maintain contact with Ash, Brock and other friends making it seem like their close bond and friendship wasn't forgotten about and pointless. Along with enjoying in Misty outspoken and feisty attitude mixed with caring, assertive side, which brought humor and tension within group being known for charismatic and lively interaction she brought.
Misty was truly unique and highly rich in personality character, she was symbol of hard work and determination, didn't let others to put her down knowing how to stand up for herself with hotheaded, sarcastic and full of passionate, curious spirit while maintaining her feminine, romantic side . Making her completete, highly relatable and with lot of depth character not deserving to end up forgotten like this.
Ill just say this: Pokemon show is dependant on his viewers, and if writers continue to ignore what makes people disappointed and frustrated, what is reason behind continuous drop in popularity with new generations of kids simply failing to fill up places of older fan which are giving up with show, than the ratings for this anime would continue to drop until they reach the point of no return,which would result in this show being cancelled.
It is obvious that pokemon directors and writers are using wrong approach of burying past, disrespecting history and pretending like it never happened, and whole strategy lately of referencing generation 1 massively through new games and show(Charizard return in main cast for BW,reuse of 4kids slogans, return of Kanto starters as mentioned before makes it obvious) is attempt to retrieve some of older fandom back.
Yet writers and producers of this show dont seem to understand how reusing Misty and making her play relevant role in anime again is something which huge number of people all around the world would like to see happen??
Guaranteeing massive hype, increase in people inzerest and excitement bringing fresh and unpredictable twist to pokemon series making it more substantial, of stronger quality thanks to paying respect to continuity and past . Along with promoting diversity and strength in characterization, anime plots and sense of world building making it closer and more interactive.
Hopefully new director(i believe he is called Tetsuo Yajima) and writers themselves will recognize appeal and potential Misty as character has, loyal and huge following and how her presence could bring benefit to storyline advancing it forward while gaining herself something from it, increase entertainment value along with attracting more people back bringing boost to ratings.