According to Nintendo’s press release, “Nintendo heads to E3 once again and brings the coverage directly to you with a two-day program from Nintendo Treehouse: Live at E3! Tune in starting at 9 a.m. PT on June 14 for a day of live-streaming gameplay focused on The Legend of Zelda for Wii U and first live gameplay of Pokémon Sun and Pokémon Moon that kicks off the program!”
There is also Day 2 which according to the company, “Day 2 of Nintendo Treehouse: Live at E3 will showcase upcoming releases for Wii U and Nintendo 3DS, including Monster Hunter Generations, Dragon Quest VII: Fragments of the Forgotten Past and Tokyo Mirage Sessions #FE! Day 2 will start with a special Pokémon GO developer Q&A at 10 a.m. PT on June 15.”
Basically it looks like the company has quite a bit of content to share at the event. Unfortunately they have not changed their mind with regards to showing off the Nintendo NX, so we guess the console will continue to remain a mystery for now.