The Galaxy S8 is not daydream compatible by default. A root access is needed to make a change in the permission file to enable Daydream support. I've read about it on a post on vrheads.com, which tried to install a Google Daydream app without success and gave them "a compatible version is missing" error. After patching the permission file they were able to run Daydream apps. So although the Samsung Galaxy S8 isn't Daydream-ready by default, you can make it work by rooting the device and changing file permissions.
Some people suggest that this is due to the Oculus competition vs Daydream, because the S8 works with Gear VR which is a direct competitor to Google's Daydream mobile VR platform. The Samsung Galaxy S8 has all the necessary hardware to support Daydream, and to be honest, it's really a bummer that Samsung hasn't enabled this by default. I'm sure that many people who plan to buy the Galaxy S8 would have loved to have an option to play games on either Gear VR or Daydream View headset. This would make the S8 appeal more to enthusiast gamers and VR fans.
In fact, if you have an Android phone that doesn't support Daydream and you still want to enable it, you can follow this step by step instruction put out by vrheads.com to enable it. It's important to note that in order to have the best VR experience as Google wanted you to have, you'll need to use a Daydream-ready phone. Patching your device to work with Daydream, doesn't mean that you are going to have a great VR experience. However, the Samsung Galaxy S8 will give you that high quality mobile VR experience, but a rooting is needed and some users probably will not want to do this to their phone being afraid to damage it and prevent their phone from booting up.
I just don't get Samsung. This really make a bad image for it, unless competition wasn't the reason why the Galaxy S8 doesn't support Daydream VR out of the box. I'm sure that there will be many users that this will be a deal-breaker for them. This is definitely a a big disadvantage, at least for those who are into Daydream VR and already bought the Daydream View headset to play games with their current Daydream-ready Android phone and wanted to upgrade to the Galaxy S8.