Out of curiosity, if it did happen, what do you think Ash's second kiss with Serena would be like?
I can kind of imagine it. Serena is coming to visit Ash in Alola, and she shows up a few episodes before Ash takes on an island challenge or one of the Kahunas (likely taking on a Kahuna). After defeating the island's Kahuna, it's night, and Ash is outside, unable to sleep because he's the thinking about the next island he's going to tomorrow. Serena comes out to check on Ash, and they talk for a little bit about the new people they've seen and the challenges they've had to face in the new regions they've been to. Eventually, Ash brings up the kiss that happened back at the airport in Kalos, and while they're both embarrassed about it (Tomato Girl, especially), they let that conversation continue on. Ash spends some time talking about his confusion when it happened and how it made him feel. He can't help but think about that moment. He wants to share another kiss with Serena because it was an experience he was unfamiliar with. Serena is shocked and embarrassed that he would ask so suddenly, but Ash brings up that he would feel weird if he did it with any other girl. Serena eventually submits to his request, and they get ready to share another kiss. Their hearts are pounding and both of them feel nervous about what's about to happen, and soon, it happens. When their lips part, Serena asks Ash how he feels now. All he tells Serena is that he feels...happy, but also a little confused. He wonders if this was how Serena felt when she did it the first time, but he knows he feels happy because he was sharing this moment with her.