My bet for Nintendo's E3, on top of my head:
Games other than Smash that we already know about:
- That new Yoshi game gets a greater gameplay overview with a late summer 2018 release window
- Fire Emblem 16 gets a full reveal with a holiday 2018 release window
- Metroid Prime 4 gets a teaser with an early 2019 release window
- Bayonetta 3 gets another teaser but nothing else
- Little to no time spent on Mario Tennis Aces, Octopath Traveler, Let's Go Pikachu/Eevee plus the ports (Crash N-Sane Trilogy, Wolfenstein 2, Okami) that we already know about, since they're all coming out this summer
- Some extra info on Kirby Star Allies DLC, Xenoblade 2 DLC and Splatoon 2 Octo Expansion (plus new DLC for Mario Odyssey)
- Konami announces whatever they're working on for the Switch
- Also a big overview of Nintendo Switch Online
Games that are rumored/not confirmed/that I expect:
- Star Fox Grand Prix if rumors come true, and if they don't, whatever Retro's really working on
- Another Wii U port, most likely The Wonderful 101
- Metroid Prime Trilogy port
- A bunch of third party ports: Fortnite, Dragon Ball FighterZ, GTA 5, Diablo 3, Fallout 4, an Assassin's Creed port (probably any game prior to Syndicate)
- Ridge Racer 8 gets revealed (has been heavily rumored:
https://wccftech.com/ridge-racer-8-switch-exclusive-metroid/)
- Pikmin 4 finally gets revealed
- A new Animal Crossing gets announced
- a Mario Maker sequel gets announced
What I expect from Smash at the presentation:
- 3-4 newcomer reveals, with 1 big unexpected hype-inducing third party character (Crash maybe?), then a couple high-caliber first party newcomers as well as a left-field newcomer, plus Inklings
- Ice Climbers are confirmed to come back (maybe Snake as well if the Vergeben's "insider information" ends up real)
- The veterans hidden in the shadows in the teaser are all revealed, plus a few other ones
- We get a glimpse of a new Story mode, halfway in between Melee's Adventure mode and Brawl's Subspace Emissary
As you can tell, I went pretty safe with this one.