The PS4 Media Player which was recently updated to support VR video playback is now set to receive an update for 4K at some point today.
The new update will allow PS4 Pro owners to import 4K video content in MP4 format to their consoles via USB sticks or home servers. The update will also add 4K VR playback for those with a PlayStation VR system. The PSVR does not display 4K but the 4K VR content will be displayed with much higher quality than what is currently shown in HD.
The update was not live, at least where I am at the time of this writing.