Seeing more details not only requires very good eye sight and looking straight forward, but also not moving the head and looking at a static object.There may be (some) room for improvements beyond 60PPD for productivity apps that require seeing fine details/text fixed in space.
But it would be wasted on things like games with lots of head, object and world movement, where not even the person with they best vision in the world will be able to really recognize anything moving at even close to a 60PPD detail level. Seeing things during movement is mostly the brain interpreting some much lower resolution perceived blur. For games it makes a lot more sense to use extra render performance to increase geometry or texture details instead of upping the resolution beyond 60PPD. So far we have only a few 4K HMDs, but these already seem to be more than enough for displaying games, while things like reading or working as a virtual monitor clearly still need significantly higher resolutions.
