It just doesn't make sense to have new content exclusive to another platform in this age of patches and DLC packs, even when we take release timing out of the picture. The thing is, I'm very confident that this will wind up getting released on PS4 as a DLC upgrade, like World of Final Fantasy: Maxima. It's unfortunate that they have decided not to be upfront about it, though.
On a side note, It's also peculiar to me to present it as a Definitive Edition if it is technically inferior to the other versions, with some very obvious rendering limitations shown in the video. Could just be a branding move, since it will assuredly be available for the other versions eventually as well. It would as if thinking the 3DS version of DQ8 was the definitive version just because it has more content in it, when it was lacking in so many presentational aspects compared to the original release.