T-Mobile says Daydream VR capability is now live on the Galaxy S8 and S8+, but it's not
However, it appears that U.S. carrier T-Mobile jumped the gun on the matter and confirmed that the last week's update for Galaxy S8 and S8+ added Daydream VR support. It's the same update that blocked Bixby remapping apps and added June security patch.
Even if it's sideloaded, the app doesn't completely install on the phone, and you'll receive an error saying that you're using an “incompatible phone.” That being said, it looks like T-Mobile made a mistake when it added the “Daydream capability” mention in the update's changelog. Or, perhaps Samsung hasn't made all Daydream support components available to T-Mobile customers yet.
In any case, Daydream VR support will eventually come to Samsung Galaxy S8 and S8+ at some point this year. Hopefully, the next time we report on the matter, the feature will actually work on these phones.
Things that are NOT allowed: