It's not 4K, though. They're not giving a lot of information, but "23M pixels" for two eyes is 11.5M pixels per eye. 4K is 8.2M, so this is 40% more pixels than 4K.
11.5m per eye is still far short of what would be needed to approximate pixel pitch of many of Apple's "retina displays" at typical desk viewing distance display well, FWIW. This a really hard problem with tech we have today.
Whether its 8m or 11m or even 15m pixels isn't the point with regards to using it to replace desktop monitors - the point is the necessary density to compete with excellent real life physical displays is really high.
Your VR monitor only ever really uses a subset of the total pixel count - it still has to spend many of those pixels to render the room around the display(s) too.
Reading text in VR is generally a horrible experience, and “4K per eye” does not equal even a single 4K screen.
That said I would be happy with 8 1080p screens.