That would be stupid, even for the internet.
Since Snake is a third party character, he HAS to be revealed before launch. They can't just not have him revealed, Konami's copyright has to be on the box, plus Konami will want to advertise Snake in Smash 4.
Now that I think about it, maybe this is why they showed a Ubisoft trophy. Now you have Ubisoft copyright without anything suspicous, then you get a unlockable hidden Ubisoft character. But I'd think Ubisoft would want to advertise a character before launch too so probably not unless Sakurai really wanted a character from Ubisoft that he just thought was unique or funny like the Rabbids. But again Ubisoft wanting to advertise...unless its a character from Ubisoft thats been dead for awhile and they don't plan on bringing back.
That trophy is just so weird. Maybe its just third party trophies, hopefully from others too. I hope for trophies from ZombiU!