I think everyone is holding onto too much hope that it will be on Xbox right away and this is the "big secret" behind the delay.
I really do not believe so. Sony obviously has something behind it, as evidenced by the trailer on the kiosk. Its going to be a timed exclusive--probably not for very long. I give it 6 months or a year at MAX.
Hellblade came over eventually; on the flip side, so did one of the Tomb Raider games to PS4(Rise?).
With the rise of Crossplay and systems becoming more about the experience, the days of total exclusives outside of first-party offerings is pretty much over. There are now numerous examples of this trend(Xbox Game Pass on PC, Microsoft having an Understanding agreement with Sony on Cloud stuff)
Extra game content or early DLC access is a bit up in the air, but even Bungie ended their exclusive PS4 content deal yesterday.