Predictions:
1. Firmware update: improves performance, adds folders, TVii for UK.
2. In-game trailer for Monolith's Wii U game.
3. Unexpected third-party title.
4. They'll mention next Smash Bros, but no footage (at best we'll get the name).
5. They'll briefly mention Retro are working on a Wii U game, but give us precisely zero details.
6. Some VC details, but still a month or two away.
Edit: I have a history of being very, very wrong with my Nintendo Direct/E3 predictions, but I do think these six are all reasonable possibilities.