DSLRBodies

• When does Nikon announce significant new DSLRs? Typically in January-March, and July-September.
• When does Nikon announce significant new lenses? Similar answer: typically February, March, July-September.
• How many DSLRs does Nikon typically introduce a year? The average was 3, with a range from 1 to 5 over thirteen years. F-mount DSLRs now average 1-2 a year since the Z mirrorless system was introduced.
• How many lenses does Nikon typically introduce a year? The average has been 5, with a range from 2 to 9 over the past thirteen years. F-mount lenses now average about 1-2 a year since the Z mirrorless system was introduced.

Thom's predictive DSLR history (updated June 2020):

With the full frame Z6 and Z7 now established, I expect Nikon to begin cutting back on full frame DSLR bodies, with primarily the D7xx and the D8xx series moving forward, and the D6 holding position until a mirrorless sports/PJ camera is developed.

Note that Nikon is shifting priorities and time schedules now. For DX bodies, I expect the D3500 to be the last entry DSLR. Whether any of the other DX DSLRs get updates is unknown, but with Nikon's pivot to the Z mount and the introduction of the DX Z50, I suspect very little activity in the DX DSLR category now.

The individual camera and lens product announcements year by year: