It feels too weird to add Serena though. Her connection is based on Kalos Ash, does he still fit with her after they changed him so much? (To me, he seems like 2 years less mature than Kalos Ash).If Iris was going to appear it would have been in Kalos. Since she didn't it kind of telling they writers probably didn't like her (or they were too busy writing their generic anime plot instead of focusing on writing a Pokemon plot which would involve them acknowledging the show has previous history...).
Though I have no doubt Serena will probably appear do to how popular she was (unless they're once again too busy writing a generic slice of life plot to bother with that pesky history thing again... or too busy trying to retcon it).
I don't think they will realistically bring back Iris, due to lack of popularity, but I just see her more realistically in the sense of her character fitting in with these other students because they aren't traveling everyday, so the story is about them and that allows for less distractions that you would get from traveling such as a typical "someone gets lost" episode.
I saw more growth of iris towards the end like when she and ash argue and ash has to apologize because she literally walks off on him. Like, Misty would just yell, but iris would require him to make up before even speaking to him first.
And seriously, Serena had cute but pointless Pokémon... I don't get what she will bring.
If they didn't change Ash so much, I would totally get it, but the series seems more cartoonish than before (and we are talking about anime... yeah really).