According to Nvidia they've already grabbed a 3X performance boost from foveated tracking. Don't worry too much about peripheral vision, Calranthe, human retinas really are utter garbage anywhere outside the center. Your brain essentially makes up everything outside your tiny center focus, using a mixture of imagination and static images captured from quick subconscious target adjustments called "saccades". Very little of what you see in peripheral vision is actually based on live image capture. As long as the system is fast enough to track the saccades (which apparently it is) then your brain will dream up your peripheral vision in exactly the same fidelity it does IRL.
So we have a 3X performance kick. Knock that up to 4X and we can drive twin 4k displays. I'd be surprised if that isn't doable in the next 12-18 months.
I think developers are still "feeling out" VR. Hopefully as the user base picks up we will see more advanced use of the tech.