It's the anime's MO to keep its protagonists as simplistic as possible, so no matter what, Ash is unlikely to be a satisfying character for us. I said at the start of the thread that I wanted him to have major flaws again, and I stand by that now, but I'm also resigned to the fact that even if they did it, it's unlikely to be as intriguing as I'd like it to be.
The recent discussion has got me thinking about how important the environment around Ash is. More and more, my enjoyment of the show hinges on the cast that orbits Ash and what they bring out of him. Put antagonistic rival characters such as Gary and Paul near him and you'll see him be competitive, hotheaded, and almost desperate to prove himself. Put inexperienced rookies such as May and Dawn near him and you'll see him be more considerate and reflective. Put normal friends and parental figures such as SM's cast near him and you get a normal guy. It's such an obvious thing, but nonetheless it highlights how crucial the rest of the cast and its ability to play off one another is.
I remember one of Takeshi Shudo's blog posts about the creation of the show. I'm paraphrasing, but he wanted to create a show that could be enjoyed by everyone, not just kids. The problem he encountered was that the producer at the time stressed the importance of simplistic characters that can easily understood by a young audience, hence the protagonists were intentionally stereotypical. However, since Team Rocket were older characters, Shudo had greater freedom with that he could with them. Hence, TR played an important role in drawing older viewers to the show. The contrast between the simple innocence and motives of the main trio and the more complex motives and morals of TR was a key factor in Pokemon's early success. Elements of this dynamic were retained in AG, where both sides interacted with another plenty of times outside of regular battling.
That element has faded as the years have gone by. These days, Ash-tachi and TR are separate entities on the cast, rarely leaving their respective "good" and "bad" labels to come together for an issue that both sides can relate to. Ash becomes a more compelling character when he's turning to TR for help to sneak into a gym, because that really highlights how far he's willing to go for a gym battles. He's a far less compelling character when he's playing the goody-two-shoes and just blasting TR off.
All of this is to say than in Gen 8, the best way to handle Ash is to give him not just interesting allies, but a set of villains that he's forced to interact with outside of basic clashes of good vs bad.