I agree completly Dawn's Story or any other characters stories are not finished
Misty and Iris never fully became the best type masters like they wanted to be
Dawn/May never became top coordinators
Max still never became a pokemon trainer
Brock is not yet the pokemon doctor he wanted to be
so there is potential in bringing these characters back maybe not as traveling companions but maybe a show like chronicles exploring what they are up too
In regards to girl pokemon trainers. Actually Misty isn't even close to water master. It means becoming strongest water trainer in world being on rank with E4 members. Because E4 members are best mono trainers in world and Misty idolize Lorelei from E4 wanting to become strong like her one day. Interesting fact us that E4 Siebold from Kalos is marked in games as water master.
With Whirl Cup and connection between "Alpha Omega of water pokemon!" title winner gets there with water master title. It was proved how winning that tournaments is needed to come closer toward water master title. Revealing there exists task and competitions you need to enter and win to reach Misty dream, just like its case with contests and coordinators.
Misty didn't learned how to use her pokemon to full potential(like Psyduck)and there exists many unexplained things about her past(like parents, bigphobia, why she wants to become recognized water master), fears, unresolved feelings etc.
Giving material to see her go on journey entering water tournaments, learning about ways of using pokemon to full potential(like mega evolution)and work on becoming E4 apprentice making big step forward in her career.
Same goes for Iris. Title of dragon master is said to be assigned by people from dragon village to exceptional dragon trainers who learned how to read this specie feelings conecting on them on such close level. That they work like one in battle as partners along with learning how to use them in most productive way. All tests and tasks in how to reach such recognition and earn title from village in Iris case wasn't fully revealed and she still has long way to go with her Axew who was enthrusted to her in order to evolve and have Iris learn dragon secrets and deepest motives, ambitions, strength that way. But with Dragonite as well still existing dissent in their bond.
But yes pretty much all of them including May, Dawn, Brock, Cilan etc have unresolved conflicts, unfinished dreams and open plots in story to warrant continuaton of their development. Playing important role in Pokemon series again.
The "anything's possible" scenario sounds cute on paper, but the writers have no reason to want to give her closure imo. They have several characters whose stories are unfinished: It'd be odd for them to choose her of all characters to show up again when she had her turn in BW.
You misunderstood. Im not advocating for Dawn and only Dawn return. Im supporting return of all replaced main characters and truthfully if i were to ask Misty deserve to return first before anyone else due to extemely long absence and having ton of untapped potential that she coud easily work as main character again.
But objecively speaking all of them deserve to remain aive and existing in pokemon whether its throug special subseries dedicated to them, recurring roles in main anime or as traveling partners again receiving follow up from where writers left their future and stories.
With current stance: "this characters had their time, new characters should always get priority". It imposes question on its own:
When will be than acceptable to return any of replaced main characters(be it Dawn,Mity,Cilan etc, etc)???
If center of attention will always and only be new set of friends Ash receives when entering new generatioin or recently replaced main characters from past saga who didn't got their obligatory one time deal(one short cameo before fading into oblivion).
When was last time we saw many of this characters ?
I have hard time believing people aren't interested in seeing writers investing more in all those characters we grew to like caring for their stories, dreams and all those fun quirks adding to appeal of their personalities.
Giving them some recognition and acknowledgment of their existence and all that potential existing inside them to deliver more mneaningfful, exciting and original changes to story.
Than any new character could in reality bring because of lacking history, established groundwork, formed pokemon team or friendship with others like Ash. To undergo bigger challenges, explore on their personalities and relationships with others on more insightful level, explore more on their past and aspirations gaining bigger substance etc.