I've been working on some backend databases for the Web site. Thought you might want to see the progression of the Z system:
Remember: right click and open in new browser window to see the full resolution.
If you're not convinced from the above at Nikon's commitment to continuously produce new Z products, I don't know what evidence you would find acceptable. We're five years in from the original announcements, and now have eight cameras and thirty-seven lenses (the 40mm f/2.8 has two versions). So call that an average of 1.5 cameras and 7 lenses a year ;~).