I agree with Fatman that this direct is going to be a big one for a lot of people even if its not just for Smash. I'm like 99% sure about one of the games being shown off tomorrow (not F-Zero), and I think people are going to be pleased. I ddon't know anything else though. I'll just post my predictions for the direct again, just so I can laugh at how good/bad I did.
The likely (practically confirmed):
Smash announcement: I think it'll be a decently big/speculated character. I'm not going to lock into Geno 100%, but he would fit the bill. Could also be someone else too. September release.
Pikmin 3 Deluxe: It's been heavily discussed already, most people think it's Nintendo's next "big" title, likely come with new content too. It would be great if they end with a teaser for Pikmin 4. I think it'll come around September/October.
Bravely Default 2 Trailer with Release Date + Demo dropping soon after. Releases around August/September.
Pokemon DLC trailer: Releases September.
Doom Eternal Switch Trailer, comes out in October.
No More Heroes 3 Trailer, comes out in October
Super Mario World Deluxe: Releases December
Mario 3D Collection: Releases November
A couple of smaller scale Japanese titles like Ys, Trails, Atelier, being shown off. Ports from 3rd parties as well.
The possibles (may or may not be announced around this time):
Maybe a teaser to Mario Odyssey 2: What better way to celebrate the year of Mario?
Mario Sports: Copyrights were found, and it seems completely logical to do.
Sonic (New game/s): They were actually meant to show something like this back in March. But delayed it to SXSW, however due to the virus they had to delay it further to an undisclosed date. Nothing else has come out about the news so far. Next year is Sonic's anniversary and I have a good feeling we are going to see a game reveal at the direct (maybe even a couple). I mean Nintendo and Sonic go pretty hand in hand nowadays oddly enough. I think the current rumors are Sonic Mania 2 and something akin to a Adventure style sonic game.
Fire Emblem Echoes: Jugdral. I know Fatman says that he thinks the next FE game will be a 6/7 remake, but I just don't think that's the case. It doesn't make any sense when 7 is already playable in the West, and most of the fanbase would prefer a 4 remake to a 6 one currently. Putting 6/7 together would be pretty hard to do unless they are entirely separated too, because the plot for those two isn't "naturally" meant to flow together.
I just can't see them skipping Japan's favorite Fire Emblem in favor of FE 6. Especially when Three Houses took a ton of inspiration from FE4, and the crest mechanic is similar to Holy Blood. Releasing 2021?
Xenoblade Chronicles 3/Monolith's new game: The core development of Xenoblade 2 was finished back in 2017, and both Torna and Xenoblade DE were done by a "smaller" team. Takahashi has stated he wants to return to X, but I think it's more likely that we'll get XC 3 before that. He's said that he wants to make a different kind of Xenoblade too. Regardless, Monolith was hiring since 2017 for a new project and it's implied it wasn't BOTW 2, I wouldn't be surprised if we end up seeing that game shown of soon. 2021?
Kingdom Hearts Melody of Memory: May or may not skip, it's still scheduled to come out in 2020 though. Depends on if Disney want to show it off in a direct or not.
1-2 new games from mid-tier Nintendo franchises. Maybe F-Zero and ???
SMT V Teaser/Trailer. Pushing it, but it's possible. 2021 release?
Bayonetta 3 Teaser/Trailer. Same as above.
Monster Hunter Switch: Capcom has said they want to create another Monster Hunter game for the "portable" audience (the Portable series of games not really a portable Monster Hunter). I think a while back a ton of decently credible people also said something akin to MH on the Switch will happen, but that was a couple years ago so it may be bunk.
Unlikely (I don't expect them, though some of these are hovering between here and possible):
2nd Smash fighter. I know, I know we traditionally have 2 fighters revealed every E3 direct; but technically speaking this isn't a E3 direct. Could go in possible, but I don't expect it to happen. Taking things one at a time.
BOTW 2: Debating on if I should put this in possible or not. But I think it's more likely that we don't see it this direct, just because I'm sure Nintendo wants to focus on Mario as their "big" thing for this direct. If it does get shown off it is 100% going to come in 2021, and I'm going to bet on the second half. I think Next year is Zelda's milestone anniversary too, so making next year the "year of Zelda" would make sense.
Metroid Prime 4/Trilogy/5: Don't expect these to be shown off here.
Possible Persona 4 Golden port? It recently came out on the PC, maybe it'll make it's way to the Switch? Wouldn't say that it's super likely either way.
KH collection: Debating on putting this in possible or not, there's a lot of people expecting it. But no one credible has stated that they are coming. We are getting another game in the series though, and it would make a lot of sense for the collection to come to Switch before then considering they released them on Xbox already.