Nikon are expected to launch the Nikon D5 at the start of 2016. It is expected to be a 20MP replacement for the 16MP Nikon D4S.
When Nikon replaced the D3 with the D4 they received a lot of criticism from press/sports photographers (the intended market for the camera) because they made a host of minor layout changes to the main controls on the camera body. This is a problem for the photojournos because they will often shoot 2-5 bodies at the same time (each with different lenses) and want to be able to swap between them seamlessly. When a new camera comes out they want to be able to use it side by side with their existing cameras.
When Nikon released the Nikon D4S they went to pains to point out that it has identical controls to the D4 - seeing this as a major selling point.
For this reason I have been hoping that the Nikon D5 will be physically identical to the D4S in terms of the layout of its major controls. And therefore would fit into Nikon D4S housings. Something I am personally interested it - as I use a D4S housing!
UPDATE. Yesterday Nikon Rumours posted some leaked photos of a "Nikon D5"
I have never put much stock in what Nikon Rumors say, well not since I had a pre-production Nikon D800 in my hand and read their inaccurate speculation about the “forthcoming” Nikon D800.
However, their Nikon D5 photos look pretty legit to me. I think that they are officially leaked by Nikon to raise some hype for the D5 (not the best week to do it when everyone is focussed on The Force Awakens!) - which is why there is a Sigma lens on it - Nikon trying to be clever!
The photos do indeed suggest a very similar chassis to the D4s. Which bodes well. There are some extra Function Buttons that are in new positions and the ISO button has been moved - which I believe it had to. I even commented in my UW Nikon D4 review that this important control was easier to use through the housing than on the camera body (which is dumb design by Nikon for a function that so defines the camera).
From a quick scan of the images, I look forward to trying it in a housing. The ISO button and function buttons looks the main hitches. But I would also expect the camera to have a high degree of button customisation - and I would be very surprised that ISO could not be reprogrammed to another button.
All that may be wishful thinking. As so often Nikon have put some bulge somewhere on the camera body that inadvertently scuppers using it in an existing housing!
p.s. Long term I would likely get a dedicated housing for the D5, just because of the workload it will get, but it would be great to have 95% functionality from the release of the camera using the old housing.