The four crystals were last mentioned in a trailer that still had Stella. And this was before Tabata was even announced as co-director. Heck, in that trailer we still had that conversation between Noctis and Stella about seeing the afterlife or something. Even after It was rebranded you XV, it was still pretty much Versus - then came the changes since they needs to get this out at a reasonable time and Nomura was just... way too busy to make it happen.
Side note here, I know people blame Nomura for this a lot but the thing is he really is super busy in that company - like he does so much stuff with character designs, the KH series, and then to his surprise he’s suddenly the VIIR director. And then they snatch his pet project away from him which, to be fair, he was sitting on for way too long, but also they just shouldn’t have announced it so soon or swamped him with so many projects and just let him work on it
But now he’s cannibalized that old vision into the KH universe so it’s all good