As far as E3 goes, here are my thoughts about it
First off, I'm predicting that they're gonna have more news about Sonic Boom, which is Nintendo exclusive.
Second, I'm predicting another big shot Smash direct and finalized release date
Third, considering the facts about how things are going between Nintendo and SEGA, and how their relationship is better than ever, Nintendo may have already bought out SEGA, and if so, such turn of events would most likely be made official at E3 rather than a direct, but this would most likely not add in a second Sonic character anyway because the game is too far into development.
Fourth, I think it's time that they announced more news about the future Zelda title for Wii U, the next installment of the Sonic Storybook series, a possible sequel to Super Mario Sunshine, another StarFox game, a conformation about the future of the Metroid franchise, GameCube games on Wii U Virtual Console, and whether or not the recent Pokemon leaks are true.