It's probably going to be fairly underwhelming, and no, I'm not saying that just to be a pessimistic asshole. Even though Nintendo confirmed there was going to be no mention of the Switch 2 or whatever they end up calling it, I do believe we are less than a year away from at least it getting announced if not just being released. Because of this, i'm sure Nintendo has some really good stuff in development to help sell and promote that new console. Based on timing, my guess is a new mainline Mario game as well as Mario Kart 9, and maybe, possibly, Metroid Prime 4.
With that said, I think tomorrow's direct will have a few last minute AAA titles to drum up one last holiday season of hype before the Switch disappears into the sunset. My guess is a new mainline Pokemon game will get announced as well as a new Wario or Yoshi game, maybe Captain Toad 2. Essentially something first party and semi interesting, but nothing on the scale of a new Zelda, Mario, or Splatoon. And finally, I think we'll get at least one new remaster style game of an old release. I have no idea what this might be, but I'd flip out if it were either Ocarina of Time 3D or Majora's Mask 3D ported to the Switch. Even better if they bundled them together, although I'm certain they wouldn't need to in order to sell a ton of copies. Other than that, I expect a lot of indie games shown off, as well as some smaller releases from bigger studios, but nothing crazy since I'm sure they're all saving their best for the Switch 2 also.