I'd have to imagine there is 0 demand for a 16mm f/2.8!
Canon already has a 15-35mm f/2.8, and a 16-35mm f/2.8.
I disagree. The 15-35mm F2.8 is a brilliant, yet expensive zoom for multiple purposes.
But there are people who need a wide-angle lense (zoom or prime) just every once in while. Therefore, they need it to be quite compact (because it is an extra carry) and comparably cheap, and the RF 15-35mm sure does not fit this description.
Furthermore, there are R users who like to shoot cityscapes at night but don't wanna get an expensive zoom. Also, 16mm F2.8 will also be great for all kinds of group photos with bad light conditions...
Don't forget those photographers that are happy with 24mm and really only need a cheap UWA option for 16-23mm. They can use the RF 16mm and just crop a little. Job done.
Last but not least: It will be a good option for those who do astro "every now and then".
From a pricing point of view, it should be perfectly in the line-up, since the 15-35mm and the 14-35mm are ridiculously expensive and a affordable 16mm is a viable option to a lot of people..
But in order to be successful, it must be in the 35mm F1.8, RF 85mm F2 price range.
Meanwhile, Sony has a 14mm f/1.8!
Comparing apples and pears. The Sony is GM lense with 1.600 € price tag. Of course, it will be superior, it has to be due to naming and pricing. Canon is aiming at a different customer group with this lense.
I Imagine Canon releasing a true and dedicated astro L prime lense somewhere in the year 2023/ latest 2024. There are a lot of patents out (remember RF 16mm F1, RF 14mm F1.4...patents in CR article) that suggest such a lense will be coming sooner or later. My guess is that it'll be an RF 12mm F2 (or 2.8 at least) in order to distinguish this prime lense from the 15-35mm & 14-35mm UWA zooms. It would/ will be the spiritual successor of the EF 14mm F2.8.