Daydream, like Gear VR, is a collection of mods to Android and it's linux kernel.
Samsung owns the mods for Gear VR, and it is unlikely these will ever appear on other devices.
Daydream however, is largely the same mods, and now available in Android N to all devices (including Samsung).
The question is: will VR developers choose to limit themselves to one device manufacturer, when basically the same functionality is available on all devices (including Samsung) via Daydream.
I think they shall abandon Gear VR faster than you might think. With Google and the community at large behind it, Daydream shall quickly become the standard (faster better cheaper, etc)
No doubt someone shall very soon make all Gear VR apps run on Daydream - that shall be the death knell ... Google may simply swallow the Gear VR team.
Still hearing crickets over at Apple ..