One of the things I deal with all the time, and which the camera makers have in spades is the "Company X should really make a Ymm lens. I'd buy it!" problem.
If the company in question is Canon or Nikon, they have probably made a similar lens at some point. They know exactly how many were sold.
For example, on the DSLR side I hear a fair number of folk wanting a fast 135mm prime. Let's call that an f/2 (f/1.8 would be close). Nikon will tell you they used to make such lenses, and they sold five different variations over the course of now almost 45 years. Total sold? Less than 100k units. In 45 years.
Another lens people want is a redesigned 200mm f/4 Micro-Nikkor. Maybe 70k units over 40 years.
Indeed, a lot of the requested lenses I hear about tend to have what I'd call the 2000 unit a year type of sales. I'm pretty sure that's not even one per camera dealer worldwide per year.
