Google initially spearheaded virtual reality on Android with Google Cardboard, which evolved into the more complete Daydream VR platform. Unlike Cardboard, which could start on any somewhat-recent Android or iOS device, Daydream support requires the phone manufacturer and Google to make sure everything works.
Unfortunately, it looks like Samsung isn't supporting Daydream VR on the new Galaxy S8 and S8+. According to VRHeads, trying to install the Daydream app will result in an error message. This could be due to a previous agreement with Oculus (which helped develop the Gear VR), but there's also a strong possibility that Samsung just doesn't care to support it.
Admittedly, Daydream VR doesn't have very much content, and Samsung's own Gear VR platform has plenty of apps and games. Still, it's annoying to see that the already-minuscule mobile VR market is fragmented.