I think it could do it if it is 1080p and 60fps. If it is 720 and 30 probably 5 million.

What if it's 720p and 60fps?

I almost got mad at this until you replied to StarDoor xD I was worried you were calling me an idiot! 

Here's what I'll say on the issue: There are certain franchises on Switch that, no matter what the systems lifetime sales are(as long as their above 30 mil) will get a huge increase in overall consumer base. And that's mainly because even if the handheld function of the Switch didn't make the system a huge success, that userbase of new handheld users being exposed to certain franchises will increase userbase. A great example is Splatoon 2. If Splatoon one was (somehow) a 3DS game then the sequel probably would have done Monster Hunter numbers in Japan. However, the current lack of stock as well as the fact that Splatoon 2 is still being introduced to handheld gamers means that the series is gaining a steady amount of a new userbase. 

Combine this with the fact that A ) Super Mario 3D Land is the highest selling 3D Mario in Japan and B ) Most people in the world have not had easy access to a 3D Mario since arguably the Wii days, and I think we'll see that interest in 3D Mario has slightly  grown, at least lifetime.

There's also the point that i've been saying since before Switch's launch, that reinventing these franchises sort of like Ocarina of Time or Mario 64, will ultimately create a boost in sales for them. 

Maybe 6 million, some people can't play games in less than 1080p. I read that in another thread. I think it hurts their eyes and their sensibilities. It isn't 2010 anymore. Lol!!!!

I don't know who you are, I only saw you start posting like three days ago.

But ...

You are quickly becoming one of my favorite users!

I think it could. I'm basing this off of Galaxy 1's sales, which were kinda close to 15m. Anyway, excited to see how it performs.

Took a five year break to pursue other life interests.

It's certainly possible.

Galaxy 1, the best selling 3D Mario, shipped 12.75 million worldwide.
https://www.nintendo.co.jp/ir/en/finance/software/wii.html

Odyssey is the most ambitious and hyped Mario game SINCE Galaxy 1, and with it being on a handheld like device like the Switch, it automatically gives it a chance to beat 3D Land as the best selling 3D game in Japan, it's beating it in COMG pre-orders thus far.

So, it has a chance. A tough one, but also a good one.

I'm gonna believe... a Mario game looking this great so early on in the Switch's life, I think it has the potential to have really great sales. Odyssey's definitely looking like a killer app title.

Hell yea