>Appeared in the story of XY
>Its flower appears in Sootopolis City in ORAS
>Its signature attack "Light of Ruin" got updated animation in SM
>It got special separate Pokedex entries in USUM

Quite regular updates for a Pokemon that GF supposedly forgot.

Also
Its a fairy like Xerneas with a blue-white body just like the head of Xerneas
It posesses deadly flower that looks just like Yveltal body patterns
It combines traits of both of those Pokemon. Even the attack "Light of Ruin" seems like combination of both of them. Light seems connected to fairy typing (see Moonblast, Dazzling Gleam) and Ruin is obvious

Is that why they're witholding Eternal Floette? Because it wouldnt make sense outside of Kalos due to its connection to Xerneas and Yveltal?