I put about 10-12.5 million though I'd say this is on the low end. My reason is that I don't see PS5 doing as well as PS4. There isn't as much enthusiasm for next gen as there was last time. I think right now scalpers are fudging interest by taking up a lot of the supply. I also expect 2021 will be a very bad economy. The COVID economy has been covered up by the media but for most of the year a third of renters could make their payments and same for home owners. As I understand it, the restrictions will lift. PS5 is going to be too expensive especially with $70 games. I think consumers are going to stick with the last gen longer. Switch also poses a nice alternative with a $200 smaller price tag. Also, Sony has burned through a lot of its goodwill in the last few years. There isn't any killer app on the horizon to boost sales either. So my prediction is a bit lower than most expect but I'm not seeing the PS5 meeting the first year of the PS4.
If there wasn't strong demand for the console there wouldn't be as many scalpers.
This isn't necessarily true. Scalpers are doing it because they perceive the product will be popular or at least in small enough supply. Also, as others and myself have pointed out before, the launch window is never indicative of lifetime sales. They always do well at launch which is why you have scalpers (make a quick buck on those people that have to have it). They're actions aren't indicative of how actual popular the product is.