They have officially retconned Ash-Greninja. They hate XYZ
Honestly, at first I was mad at Journeys/Tomiyasu because I thought it was their idea but now that I saw that it was indeed "retconned" in the new games, it's obviously a choice coming from Game Freak/TPCi and it make perfect sense to me.
It's a form from an anime series that is not airing anymore and is from 6 years ago, TPC probably didn't want it in their new games because it's irrelevant now. Maybe we will see Ash Greninja again in a potential X/Y remake, but it's probably 6-7+ years away from now.
At least, be happy, we now know why it wasn't in the Greninja episode and the form is still in Smash so that's something lol.
Regarding Amourshipping, I'm a bit sad because Serena was part of the reason why Ash mastered the form in the first place , all this work and beautiful writing from the Snowbelle city arc for it to be retconned 6 years later... Truly sad.