Before Smash Bros was released, there was a video where Geoff Keighley which he is one of the judges at the Smash Bros. Invitational tournament interview Hideo Kojima about Snake returning to Smash (video start at 29:00):
Did you know that the MGS composer Nobuka Toda was on the composer list on the Smash Bros website?
Did you also know that a Gamespot Interview back in 2014 where Gamespot asked a representative if Snake was going to be in.
He respond to him by saying this " We have not announced Solid Snake." Then Gamespot say " So a big question mark?" They really didn't denying or confirming that he was going to be in. Maybe they are holding him for a big, sneaking surprise which nobody know. I don't know what going to happen next, but we see.