According to recent rumors surfaced on the web, Nikon is working on the D850 successor and it will be named as Nikon D880. As mentioned before this high-res DSLR is expected to be announced towards the end of this year.

In addition to the D780 DSLR announced by Nikon at the CES 2020 event at the beginning of the year, the company will allegedly update its another FX-format DSLR. If all goes well, we might meet the Nikon D880 (name is not confirmed yet) in 2020.
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https://www.dailycameranews.com/2020/01/nikon-d880-coming-in-2020-first-specs-leaked/