Of course, I don't have any inside knowledge of Nikon plan but here are some speculations for the fun of closing this 2016 and looking into 2017:
- D820: a 50+ Mp sensor inside the D500 body with the CAM20K AF for Nikon to compete with the high resolution market that now includes the new medium format players
- D780: as the D810 is retired from production, the body platform of the D760 picks up the 36Mp slot while retaining the CAM3500 AF- basically a D810 in the smaller D760 body.
The D500 body is essentially the D750 body, just some different types of switches/wheels on it. So, I suspect you're right, but I don't think Nikon will go 50+, I think they'll use the 42MP BSI sensor from the A7RII. Two reasons, one - it is a fantastic sensor, probably overall the nest made, second, generally Nikon only introduces one new Sony sources sensor and one of its own over a product cycle, and it's already used that R&D budget with the D5 and a sony special for the D500, so I expect the rest of the range is off-the-shelf Sony. I think the BSI capability will more than make up for the slight deficit in resolution compared to the Canon, and it will likely be a faster camera, too.
Whether they stay at 24MP or make the jump to 36 for the next step down is interesting. Not sure what they do.
- DF2: anniversary retro design with ergonomic improvements from the DF. This model would get the 36Mp sensor also, as well as the better CAM3500 AF module.
Can't see it, I think the DF was a one off. If they are doing an anniversary special, it's more likely to be an FF mirrorless, with a short variant of the electronic diaphragm/AF-S version of the F mount (with simple adapter, like the Canon EOS-M mount, probably in the box) posing as a revived Nikon S series
- D620: taking over the D750 position, retaining the 24Mp sensor, but getting the better CAM-3500 AF.
I'm betting they'll pass on that. I reckon that the D750 was the planned D620, the marketing department had a last minute wheeze of branding it as a new series. The range looks too crowded as it is.
- D5X may be announced in 2017 for delivery in 2018 with a 60Mp to claim the top resolution in FF land and a D5S also in 2018 with improvements to the present 20.9 Mp sensor.
Can't see a D5X, that ship has sailed. D5s for sure, there is always an 's' version of the top range model. (the others too, they just change the naming convention, so the D800s was called the D810 instead)
- D900: late 2017, with the present 20.9Mp sensor inside a D500-like platform, the way the D700 was to the D3.
That wouldn't be like the D700 was to the D3. D5 and D500 are completely different cameras. I can't see it happening, either. Just makes everything too crowded. It would be extremely similar to the D760 (which as I say is essentially the same platform as the D500)
A busy enough plan for Nikon? ... nice to speculate but I think Nikon will only do half of this in the next 12 months. Cheers and Happy New Year to everybody.
They will only do half of it ever. No 'D900', no D5X, probably no D620, possibly no follow up to the Df