There are fewer references to previous pokemon seasons in this series than there are in every series before and after.
It's not just about nostalgia, it's genuinely immersion breaking when ash might as well be an entirely new character, every event he experienced prior to XY is almost irrelevant.
Literally the only things that ever come up and become directly relevant are episodes from the tail end of Best Wishes that were made specifically to promote XY in the first place.

It feels like a weird gap in the story, no pokemon from previous series, no even MENTIONING his pokemon from the previous series.
If you look at the wiki page for any of ash's pokemon, there's just a sudden gap between BW and SM. At this point they might as well have had Calem be the protagonist instead of Ash. Nothing intrinsic about Ash Ketchum continues into XY.

It's good to not just be a nostalgia wankfest showing reference after reference marvel style, but it's another to straight up pretend the past doesn't exist whatsoever