One way or another, Daydream will work on the Galaxy S8.
Update 5/17/17: Google has announced Daydream support for the Galaxy S8 will be available via update this summer!
If you try to install Google Daydream on the Galaxy S8, a phone that exceeds the requirements for Google’s VR platform in every conceivable way, you’ll be met with an error message stating a compatible version is missing and will not be able to install Daydream. Just like we were, when trying this out during the event in NYC.
The bad news — a compatible version of Google Daydream doesn’t exist for the Galaxy S8.
The good news — that isn’t going to be true forever, but you’re going to need to wait a bit.