Highly recommend taking a look at the Sony lineup, particularly the A7S mk II and the just released A7R mk II (S would be better for video).
The A7S is amazing in terms of low light capability. And the A7R is unmatched in resolving power.
If all your glass is Nikon, you can get a Metabones adapter for roughly $700 which would do the job giving you a Sony to Nikon mount thats tack sharp.
While not reflex, the OLED viewfinder is superb, you really have to see it to believe how sharp it is. And the swing out monitor on the back which rotates up and down, is fantastic for doing handheld video work above head or down low.
All of the new glass that is coming out, 70-200s, L-Series, Zeiss, they are all making their lenses for Sony... the new beast in the low cost camera lineup. (Body under $5000)
A final note, most people think Reflex (SLR/DSLR) is superior to non-reflex, but in fact the opposite is usually true. Compromises must be made for the reflex mirror system and curtains, which mean the engineers must make concessions when dealing with the optics and the plane of view.
In truth, the sharpest cameras ever made, are non-reflex. The Hasselblad SuperWide is considered the sharpest lens ever designed to date (I love mine and still use it to date). The lack of a reflex finder isnt really an issue as it's wide. With todays digital backs, and a led viewing system- it's really the way to go.