These are some pipe-dreams, ordered from most likely to least likely:
- MARIO MAKER FOR SWITCH FOR CRYING OUT LOUD (Actually, I think this one is fairly likely).
- Twilight Princess and or Windwaker HD port for Switch. (Better yet, bundled together for cheaper).
- 2D Zelda Trailer for a game next year. For Switch. Though I would be okay with it on 3DS, I find it unlikely that this game (which will happen, just maybe not this year), would be on anything other than Switch. I want something with more traditional dungeons, with open-world still.
- Something really impressive from Rare about Sea of Thieves. I don't know if they can really do it, but I want that game to succeed in the long term.
- Breath of the Wild Sequel, like Majora's Mask. Smaller, reusing the assets and engine, with a dark tone and heavy emphasis on story. Set to release next year sometime to tide us over.
- Paper Mario. A new Super Paper Mario, or Paper Mario TTYD sequel. Not like the two most recent. So, call it, "Paper Mario 3".
You can tell I'm a Nintendo fan (Switch, no Wii U) and I like Legend of Zelda.
Also things the OP mentioned, Classic Games on Switch stuff, FF7 footage, Metroid Prime trailer. (I'm assuming on that last one. It will obviously be there).