Here we go 35 minutes!
But like the E3 presentation, about 20 minutes of that will be dedicated to Smash.
3DS - Possible announcements could be a port of the Dragon Quest 1, 2, or 3 games. They were all released in Japan only on 3DS. Perhaps a physical copy of all three BoxBoy games together and the BoxBoy Amiibo. Mindblowing with little chance of happening would be Touch Detective 3, Chibi-Robo 3 and/or Ace Attorney Investigations for the eShop. Surprise new upcoming release - a remake of Link's Awakening for both 3DS and Switch. Will Partners in Time be the M&L game to not get released for the 3DS or might it actually get a 3DS remake also? I could see an announcement about a special edition 3DS /2DS being released in a couple months for the holiday season. I think Japan had a couple nifty looking designed 2DS units that haven't been brought over to NA. My biggest worry: There will be an announcement about a change or end date of the 3DS's free online gameplay. Looking online, the upcoming 3DS games of 2018 are Luigi's Mansion, Yokai Watch Blasters (in 2 days!), Etrian Odyssey X, Treasurenauts and The Unlikely Legend of Rusty Pup so there's a chance these get some brief clips and firm release dates.
As for Switch and Smash Bros., I think a new trailer will probably be shown and that's it. There is still the possible "Spirits" mode to dive in to but another Smash Direct seems more likely to tackle that. With the XC2 DLC about to release, I could see another mention of that in this direct leading to a possible Smash reveal of Elma from XCX. Otherwise, Luigi Dude's suggestion of more Let's Go Pokemon information leading to a new pokemon for Smash reveal seems to make the most sense. At this point, that's the only hype I'm creating for myself in the Switch department so Nintendo's got the chance to really surprise me.