(SR5) There is no 4K photocamera coming from Sony at NAB. A7rII coming after NAB.
If you were waiting for a new A7sII or any other 4K pro photocamera (not camcorder!) than skip the event. There will be no such camera at NABshow. The other rumored cameras like the A7rII and compact cameras will be announced after the NAB show.
For filmmakers: Sony will announce the HDC4300 at NAb (all info here at SAR).