There should be at least 30 million Nintendo Switch owners by December 31st (hopefully over 32), so Super Smash Bros. Ultimate pulling off 9 million copies in 24 days, would mean that only 30% of the NS userbase has to buy the game in its opening month. I think that 9 million world wide in barely 3.5 weeks, would be an awesome achievement. That being said, I definitely would love for something uncanny to happen, like 16 million copies sold in that amount of time.
Personally, I have six copies of the game on pre-order (and will probably get more between now and launch). The reason being, all of my friends buy their games from me, thanks to my Best Buy Gamers Club account. Some already have it pre-ordered, elsewhere, and others are planning on getting it from me once the game actually releases.
It’s gonna be huge!