Yodobashi Camera reports that they are completely sold out.
First time ever for a Nintendo game.

Worldwide the Super Smash Brothers series is about to become the best selling video game fighting series of all time.

Currently:

#1 - Tekken  at 47 million between all titles.

#2 - Street Fighter at 41 million between all titles.

#3 - Super Smash Bros. at 40 million between all titles pre-Ultimate.

#4 - Mortal Kombat at 35 million between all titles.

https://en.wikipedia.org/wiki/List_of_best-selling_video_game_franchises

I'm a bit surprised that Tekken is ahead of Street Fighter and Mortal Kombat, I didn't realize it was that strong of a franchise.

Tekken has 7 mainline entries vs Street Fighter's 5 so that's likely why.

The series was huge during the ps1 and ps2 eras. 

Street fighter has released on way more consoles and has a load of spin off series. Tekken was predominantly on Sony consoles for years.

Yup, especially the PS1 era. During that time it was a legit system seller around the globe.

I know, I guess Tekken has been more consistent over the years while Street Fighter has had massive ups and downs.

Another day! Another record to be SMASHED!

Probably over 2 million in the US. It outsold all previous Smash games and Let's Go in Britain. 4 million first week seems like the lowest possible guess assuming Europe overall just had low sales relative to the other regions and the US didn't outsell Japan by an even larger margin.