This is LONG post, so i in advance thank anyone who has enough patience and desire to read through this.
But for this topic short, moderated answer wouldn't imo give elaborated and enough explaieed review on key issues pokemon anime is faced with and what approach should be taken to make it more enjoyable, meaningful and captivating to follow.
With this type of questions its hard to make non biased response, because whatever we believe might improve quality of anime appeal and its storyline is at least partially influenced by our own desires and wishful thinkings. Therefore not guaranteeing how our suggestions would indeed strengthen character development, consistent following and thrill of journey itself in pokemon series.
But for the sake of discussion ill list what in my mind would help to push anime in better, more engaging direction. Meaning increasing its continuity, offer deeper, more concrete growth of characters, dash of unpredictable innovative ideas which would shake things up breaking down stagnation and monotony. Along with maintaining connections to history and past influencing characters adding to credibility of Ash journey and consistent following staying faithful to previous growth and unity which keeps Ash linked with everyone else.
In as much increasing depth of tale pokemon anime seemingly promotes.
To start things of:
1: -Shake up current way Ash character has been handled and plot which focus around his journey of exploring new regions, cultures, traditions and various people. Provide indications of all his previous effort, struggles, training and learning on mistakes was worth it bringing him closer toward accomplishmernt of his own dreams and ultimate quest of becoming pokemon master. Such as having him win regional league for change with new grounds being break with it. We all know how winning one league is just tip of iceberg in what his desire of becoming best pokemon trainer in world and pokemon master entails. After that there exists champion lesgue, challenge of E4 and battle with champion.
Which is also just one of steps required to be accomplished on road of becoming pokemon master as evidenced by E4 Lucian from DP saga. There are plenty of other regions afterwards to explore, make name for yourself amoing other trainers and develop all kind of even better, more ingenious battle techniques following principle of "we continue to learn and expand our knowledge through whole life". In order to become worldwide famous and truly best.
In fact after champion league there could easily exist other, more challenging tasks like some sort of league for trainers which managed to win championship gathering only those worthy enough to enter such intense events and through selection choice face various tasks and evaluators until only one is left(similar to eay BF worked with only exceptional trainers getting ticket to get there).
Expand on Ash connection with Ho Oh and why he was deemed as creditable and special enough to show himself to it. Dig deeper in Ash past bringing more dimension to his character, potential fears and repressed resentment he may have felt for issues with past which he tried to forgett. Like whole thing with father which could play important role in Ash life and offer gateway toward great development. Giving to viewer extraordinary experience of different take on Ash growth being taken.
Whole issue of Ash father was also brought up in that for some infamous interview with mr. Hidaka from 2008:
Who is Ash's father? This one made him laugh, since I asked it rather bluntly and simply. He explained Ash's grandfather was a great Trainer who traveled the lands a long time ago, and Ash's father followed in his footsteps and left. Then I asked if he would ever appear, and he responded that only if the writers felt a need to "grow" Ash as a character (personal note: we need some character development, please).
All of this would make Ash long journey more believable, filled with content and bigger quality on strengthening its connections to past and making it treated like continuity based show. Rather than some weird compound full of fragmented pieces of development scattered all over the place with no real plot or history behind itself.
Inciting enthusiasm among viewers how long story of Ash travels, learning experience and established strong bonds with various characters leaving impact on him has sense of progression making journey all that more believable seeming like story is actually going somewhere.
2: -In alignment to that writers should keep ties with previous sagas, anime history and friends which played important role in Ash life.
Staying faithful to message pokemon series promote about show which is supposed to be treated as entity which builds on itself paying attention to previous characters and events making pokeworld feel more closer and connected. Acknowledging how they have their stories and unfinished dreams too, how there exist close bond which should tie Ash with them with friendship and impact meaning something in end. Rather than being forgotten about never to be seen anymore, enjoy in their unique antics and divergent personalities with effort and plots staying acknowledged bringing everyone somewhere eventually.
Have them play some sort of recurring role coming in future sagas for their goal/story purposes interlacing story path between them and Ash meeting at some point joining company for awhile(like N did). To catch up on missed time, see them develop more and help move current story forward tying their dreams into it when they could benefit. Have bring unexpected surpruse with their return making dynamic more lively and varied thx to their presence.
Like Misty who i would like to see back the most. Not necessarily just because she was among my favorite companions but also because she was absent since 2005 being great character with lot of personality and some update would be welcomed being interesting to see how she would work in today anime format. Having unfinished story and unused potential which gives character required stamina and material to put her to good use again (like her goal never becoming water pokemon master rquring traveling and entering events like Whirl Cup was to spread your name worldwide and sharp skills coming closer toward such title, many unanswered things about past like parents, why she likes water types wanting to master them, why she fears bugs etc) ,. There is also whole admiration toward Lorelei and E4 members offering whole new angle through which her dreams could be tied into it and gave deep character development.
In sense of trying to becoming E4 member tying her quest directly into it( of becoming best type trainer, something E4 are) and introducing tasks or evaluators she would need to pass to determine if said character has potential for such thing giving her some quality development, potentially facing dilemma and fear if she is up for such task and where she really belongs in trainer scene.
In form of logical progression from curent position of filling in for sisters and taking care of gym bringing outlet to push her story to next level
and serve as massive step forward in bevoming honored and recognized water specialist thus bringing her very close toward achievement of water master dream. Along with giving us fresh new way to see someone getting developed , promote pokemon and leave mark on storyline making it richer.
Someone spunky, fiery and perky like her would certainly light more spark, tension and enthusiasm in cast through wide diapason of emotions she can produce imo.
Not just Misty, all of previous companions should be returning for special arcs or joining main cast for season or two letting viewers know how they are not forgotten and how all their growth, influence they left on plot and Ash character, strong friendship they have with him contributing in anime building on itself wasn't for nothing.
In general return of popular all time favorite would be fresh and unpredictable twist to pokemon series pleasing many older fans and giving something new and unpredictable for younger generations sparking their interest to find out who they are helping them to better understand Ash past.
Since experiences from past give watcher insight in foregoing and coverage on amount of growth and hard work done prior to reaching point on which characters and story are standing right now.
Such approach would not only be generous gesture for new generations giving them insight in pokemon history with current story being enriched with more "meat", but it would also make older fans appreciate anime to higher degree serving as nice throwback to past improving anime storyline.
3: -Reduce repetition and rehashing of previous ideas. Like repeat of same situation with every Ash fire starter being neglected, abused by previous trainer managing to overcome its issues and grow under Ash tutorship. Pikachu refusing to evolve. Predictable cycle of rivals always having faster learning curve than main protagonist until they get defeated in final confrontation. Rather than more innovative approach such as rivals themselves being less talented having to catch up to main protaginist level bringing new twist in story. Main girl having fight with Ash just to later in same episode peace things out applying same formula on her legatee.
Team Rocket constantly following same principle of trying to catch Pikachu on never ending futile quest which last for decade and half. Serving as comic relief which gets blasted off. Etc, etc.
For instance why not make Giovanni and existence of TR organization play more prevalence in pokemon world as whole, have them clash with new regional organizations like Team Flare or any other future crime groups in fighting for predominance. Affecting Ash, his friends and everyone else lives on more groundbreaking basis effectively bringing another plot through which protagonists could be more actively involved. Reducing on episodes with no content, repetitivity and no real prospect of things changing from stagnating point.
Like i brought up before unpredictable twists, at times change of direction in which events and characters are being taken and fresh surprises from past building on plot suspense are desierable for long running serie like pokemon. In fact even encouraging to have eventful story, strong plot which builds on itself maintaining continuity and ties with past supporting its credibility, more substantial sense of moving forward and true charm of journey where main characters explore wotld, work toward dreams and have legacy left behind.