Don’t hold your breath for 5K video from a Nikon DSLR as 12 bit 1664 x 1100 resolution is what is provided right now. But the live-view stream is 4992 x 3280 pixels and it should be available to be captured. Even if live-view is captured, it would likely be at a lower frame rate than 24fps.
When the Magic Lantern team first started capturing live-view on Canon cameras they were not sure what they could do with it but they quickly made it into very useable frame rates. So it will be interesting to see how this development goes.
You can view the thread about this raw video hack on the Nikon Hackers forum and below is a raw frame example of what they have done so far.