The YouTube upload of the song is just "12"...
HOLY CRAP GUYS STREET FIGHTER'S TWELVE CONFIRMED FOR SMASH /s
That joke could've worked had it not been for the fact that everyone was right about that Castlevania song screw-up.
In other news, here's another rumour for anyone interested in entertaining their speculative minds:
This leak came from 2ch (japanese textboard), and apparently has been there as far as January 2018 goes.
Spoiler: Character list (click to see content)
Now, this leak has gotten quite the discussion, as you can see in here:
This is the January leak: https://gamefaqs.gamespot.com/boards/234547-super-smash-bros-ultimate/76899877
It was debunked on the basis of the site's whois (credit to SourceGaming): https://twitter.com/AllSourceGaming/status/1029134656845766657
But there are several arguments that suggest that the leak is legitimate after all:
It has an active patreon with supporters: https://www.patreon.com/2chwin
The archive updated again as scheduled: http://www.2ch.win/aotd.html
It has a huge discord that has history dating back years: http://discordapp.com/invite/5kug84s
Small scale board archiving services often change domains to avoid trouble (their discord even says they do this): https://i.imgur.com/u95za7k.png
The site seems to be directly linked to 5ch: https://premium.5ch.net/
None of this is surefire proof that it's not fake, but it's enough to not completely write if off imo.