Being in the Biz for a long time and as Nikon Pro, I won’t mention any sources, but the grape vine is long and perilous…Nonetheless, I am quite sure Nikon has been anticipating the Canon 5DS for quite some time and will respond in kind in the next three to four quarters with something mind blowing.
I am quite sure that Nikon has already a launch date for their new Nikon D900. It will be an updated iteration of the D800 series of cameras and have a a 54 megapixel sensor that will sport a new high speed processor capable of pulling out a very good 12800 iso image and an excellent 3200 iso low noise image. It will allow for an extended iso range from 50 to 51800. It will not have an anti aliasing filter. It will do all of this at 6 -7 fps in RAW and video will be capable of 4k rendition. I suspect to see this version out in the Spring of this year. The Nikon D810 will remain in the line up.
Sony 54 Megapixel Sensor Link.