I inquired to KayzEye about a focus screen for the D600. Here is the email I received:
" It is good to hear from you and I hope your D7000 has served you well. At this point, we have not yet had the opportunity to study the D600, so I cannot say with certainty. However, given the difficulty we have encountered with the design of Nikon's recent full frame cameras, and the unavailability of Nikon parts for use in R&D, it is unlikely we will be able to support the D600 model. I will keep your email on file, and if there is any news regarding the D600 camera, I will be sure to let you know. Thanks again for your interest in KatzEye Optics products and if you have any other questions, please feel free to ask."
I hate when people ask me what I see myself doing in 5 years...... I don't have 2020 vision!