The upcoming Nikon 1 J5 mirrorless camera is rumored to have 4k video recording capabilities. If true, this will be the first Nikon camera with 4k video. The official announcement is expected in the next few weeks.
In a interview last year, a Nikon representative talked about 4k video being "a bit tricky".
The Nikon 1 sensor is capable of 2k and 4k video recording.