That's not a thing that happened. They weren't like that. See, the big thing about all of those peopl- Shinichi and Conan aren't a couple. Not only is that selfcest, but it's also pedophilia. Preeeetty sure you meant Ran and Conan, or even Shinichi and Ran. Anyway, those couples mutually liked each other and it was very obviously right there. There was no mistake, love was in the air. Outside of some 4kids magic, that was not the case with Ash and Misty. This all smells awfully shippy to me.
Awfully shippy, indeed. You seem really fixated on very subjective things, like May's beauty that "overshadow all girl", which many would disagree with (including me), the whole idea that beauty is even a factor, and your feelings towards Serena.
First off, I still really don't see anything that would push for romantic developments in XY&Z. Second- actually, I think Hiroshi said it best, 's not relevant.
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But as far as the Korrina is concerned...I doubt they'd get rid of Serena and Clemont, largely for the reason that I mentioned before. They are the dynamics and Ash is the constant. Granted, the character development in Pokemon is pretty bare bones, but it's there, and Clemont and Serena can't leave the party until they've learned something. They're dynamics for a reason: they change. Just starting the season with, "Whelp, it was fun Ash but maaaan a bed sounds good right now," and then boom, a new party, would be...odd. Very odd. It'd make the viewer wonder why they tagged along in the first place, and that would make the rest of XY seem marginally less significant. They need to hit a milestone before they leave, because in a lot of ways, their journeys are made to develop and even end before Ash's.
Alain, from what I've read, seems a lot closer to a rival (or maybe a sidekick/protag in a much edgier Pokemon anime). Certainly no replacement for the male character in the show, it'd never work. Ash would be completely overshadowed by the guy, and that, for a show like this (and this show in particular), would be very, very bad. And as for Korrina...what does she have to offer the narrative. I could see her as a major character as a threat to Lysandre, but not one of Ash's party. There's just no point. She has as much reason to be there as...
...I dunno, Ash's mom?