Where did you read that the future Gear VR will have its own display? I don't recall seeing that anywhere. And I think the only reason to put 4K into a smartphone display right now is specifically for VR, as 4K is unnecessary overkill in a smartphone not used for VR.
This isn't where I read it from but it's one of the first links that popped up from a Google search. And I agree with you about the overkill in the s8.
http://www.popsci.com/samsung-gear-vr-2-rumors-features-wireless
SAMSUNG'S SECOND GEAR VR MAY BE A STANDALONE WIRELESS HEADSET
NO NEED TO INSERT YOUR GALAXY PHONE OR TABLET