Mac's are already powerful enough for VR. Source: I'm a Mac developer developing for VR.
Now, this is a fact that goes against the consensus: The Oculus founder said Mac's can't run VR. Surely he's not lying?
Well, here's a fact: the Oculus "able to run" requirements are not based on performance, but a preset list of GPU's (allright - partly valided and added because of their performance).
But my point is, that because the GPU's used in say, the hi-end iMacs or Mac Pro's are not in that list, the Oculus runtime will refuse to run. Even if the GPU can handle the game in 90Hz just fine. (I'll bet that if you used an older version of this runtime - you can't even run Oculus with Nvidia GTX 1080 - because it's not included in the list!)
That aside, more power will definitely help. Especially with experiences that go beyond trivial demos or basic experiences. The RX 480M will definitely be able to power a lot of VR experiences with good performance. In any case, I believe Valve will add Mac support first since it's more close to their interests (Steam Machines & Linux).
It's always funny to read posts about how Mac's can't run VR, when you have such a big push from Google and Samsung for VR on Android phones. Or do you think the Galaxy smartphone graphics chip is on par with GTX 970?
If you're interested in more about VR on Mac, you should sign up here:
http://www.vrdesktop.com/