It's a big ask. PC sales will help it but may still not be enough. Im going with the 5-6 mil range.
Also, we may never know final sales if Capcom choose not to reveal or update sales down the line.

I was thinking it would sell like 5m in Japan. However, we are also looking at a generation where basically every gamer in Japan is on the same platform. That could end up boosting sales quite a bit. I really don't know what is going to happen.

That's global sales, though combined Japan sales should make up around 7 mil of those from what I can find. I'm certain there was a ton of double dipping here though and if Rise goes the DLC route it won't get that.

Still it is a point that I had considered as well and while I don't think the original MH4 had ever reached 7 mil if it had sticked with a single version, it could have gotten closer, so it's by no means unimaginable that Rise could do it if the switch factor kicks in.

Rise doesn't get double dipping but it gets the home console fanbase as well, singular versions would have at least hit 6m they were already knocking on the 5m mark with the frequent releases. It's not really Switch factor that's needed here just Capcom's own handling.

But isn't being able to appeal to both home console and handheld gamers part of the "Switch factor"?

Also while I'm not an expert on the subject I'm not sure it makes sense to make that clear-cut a division between home console and handheld MH fans, especially since the series mostly went full handheld between Tri and World which was almost a decade. There are obviously going to be some who stick with one or the other, but my assumption would be that the majority of fans are into both. Not denying that it's an advantage though, I'm just not sure how big of an advantage.

Home and portable fanbases are very different as the one major difference which defines why the portable games have always sold more in Japan is the portable ability to allow lan style gathering parties. This social element created a sub culture similar to the likes of Pokemon over there and is something consoles can't emulate even with online until the Switch it's like dungeons and dragons to the fans in Japan this is on top of the portable variant suiting the longer Japanese days out the house whether someone is working or going to college and such hence why a lot of portable MH fans in Japan are students who are the the main group who engage in the lan style gatherings.

This is why no console version could match the portable versions sales in Japan World's director touched on this to investors before Rise was announced in that World was not being bought by a large part of MH's fanbase due to not really catering to to above mentioned elements he even mentioned the student demographic.

Interesting, and it fits well with how handheld systems are just in general much bigger in Japan. It's certainly true that the handhelds entries have wider appeal than the home console ones and it makes sense that a hybrid game would have even wider appeal than that, I'm just still wondering by how much since Rise will be the first game to test that.

I said 6.5 million.

Seems like it probably did over 2 with digital in first 3 days from initial reports. By the time launch sales cool down (let's say end of April) it could be 3 million. Perhaps 4 million by end of year. Could see it passing 6 million in 2024. 6.5 million might depend on if Nintendo puts off the Switch successor past 2024.