On the bright side since the anime will go on forever you can make up any ending you want for ash's life and keep adding to it as new characters from new gens appear, personally i'd like the way they end together to be extremely awkward but wholesome, with everyone meeting again in passio after a timeskip for a tournament
>On one side Clemont, Bonnie, Goh and Gary trying to get serena and ash together
>On the other Koharu, iris, may and cylan trying to make Dawn and ash get together
>The alola gang mostly unaware of everything actually spending way more time with their champ
>After many awkward moments brock steps in to help, dawn and ash have a moment that ends with a kiss
>Ash has no clue what to do next but a good talk with misty allows him to clear his mind
>Then some antagonist like a bunch of UBs or maybe rainbow rocket attack and beat everyone except ash dawn and serena
>Ash is in real trouble and serena starts worrying but dawn steps in to support ash and tells Serena that everything will be fine
>This makes serena realize that dawn's trust in ash in a whole other level
>after the day is saved ash and dawn are trying to confess to each other
>now Serena tells dawn everything will be fine
>so while everyone is watching ash and dawn finallly end up together getting the courage to confess to each other at the same time
i just think both of them have great chemistry but both of them are too dense they would need a ton of help to end up together