Ever since the Direct Mini, people have been obsessing over a full direct coming soon. Well, it didn't happen. But now that we do have one on the horizon, nobody seems to know what will be shown.
Considering how big Super Smash Bros. is, I highly doubt it will be shown in this Direct, but rather be held back for E3 if they decide to show anything on it at all, whether new game or Smash 4 Port. Personally I'd be fine with either one. And same goes for Metroid Prime 4, especially with how long it was between 3 and the announcement. People say a new Pikmin might be revealed, or more info on Pikmin 4 instead, which I could see.
Things I DO expect though, are more WiiU ports, more indie reveals, and most importantly, more information on the Switch Pokémon game. I expect it will still resemble older generations in terms of how it works: battle system and so on. I also expect (with a LOT of hope behind it) a Yokai Watch news bit, whether Busters, YW3, or anything else.