My opinion...

On Youtube, someone named TheChornick made a video about why Misty will not return to the Pokemon Anime. While he did make some good points, that does not mean that Misty can't guest star in the Anime, like she did in the Hoenn and Battle Frontier season, or star in her own Pokemon Special Episodes like she did in Pokemon Chronicles. Other shows like Kamen Rider, Super Sentai, Yu-gi-oh, and Fuller House have had past characters show up every once in awhile. So I see no reason why the people responsible for the Pokemon Anime can't do the same for Misty. True Misty doesn't have as many goals as Ash's other female friends do, but fact remains, being a Gym Leader is a big deal. And we could see her do stuff like catch and train more water Pokemon for her Gym and Gym battles. Or see her winning some kind of contest her Sisters are a part of to not only show them that she is just as good as them (if better), but so then we (or at least I) can finally see her Sisters give Misty the respect she deserves. Misty could also be in a Pokemon Tournament for gym leaders and show just how good she has become. So to make a long story short, there are plenty of things that can be done to bring Misty back as a guest star, or the main character of a special episode every once in awhile. The people responsible for Pokemon just need to think of something, and do it.