I think this Direct will offer us a clear indication of how far we are in the first-party transition away from the 3DS, based on the nature of whatever is announced for early 2018. We know that oddball first-party titles like Sushi Striker are still on the way, but tomorrow will be a bellwether of whether the recognizable Nintendo IPs are effectively done with the system after late 2017's trinity of Metroid, Ultra Sun/Moon, and the Kirby anniversary game that is certain to be the 3DS flagbearer in the show. (Certainly not complaining if Advance Wars shows up out of nowhere, of course; after 2D Metroid it was the absence on the 3DS that was the most deeply felt, even amid the unprecedented attention lavished on its sibling Fire Emblem.) It's been clear for a long while that EPD is pretty much off the 3DS, with the known IPs this year coming from Arzest, MercurySteam, Game Freak, HAL and so on. But regardless of who the developers are, I kind of wonder if there's anything left to do with familiar Nintendo series on the system, as it seems all the active ones have already stamped their presence and moved on.
That said, like many here, it's the Switch library heading into early 2018 that is the truly tantalizing unknown, and Directs typically come with at least one significant first-party announcement not hinted at previously (sometimes including external collaborations on Nintendo IPs).
I don't think we'll see Retro's game or Prime 4; one or both are likely positioned to lead the next E3.
I'm rather bullish on hearing from Platinum at last, and practically anything out of them, from the safe and sensible (Bayonetta 2 port) to the risky and rapturous (W102) to the impossibly outlandish (my long-running fantasy of a three-way Bayonetta-like deal with Capcom to bring us Viewtiful Joe 3) would qualify as good news. Pretty much anything is fair game here, including ports of the likes of Vanquish or Revengeance that are already in the PC portfolio, or a fresh take on an existing Nintendo IP. The least interesting outcome would be a small licensed television tie-in game, but come on, Nintendo and Platinum know the audience for their work together and we'll get something more targeted than that.
Not about to venture any guesses pertaining to Animal Crossing, though I will say that so far, we don't know what the first-party mass-market flagship will be for the first half of 2018 (it's likely to be something bigger than Kirby or Yoshi in mass appeal), and there are only a few IPs that fit the bill. We all know it's coming, but it's still early days for the platform and we don't know how the full game will be aligned with the mobile app.
We can reasonably expect that something online-centric will land in the first half of 2018 to give the online service a push as it transitions into a paid model. I know many expected a port or complete edition of SSB4 to fill that role, but I think its window is passing and we're likelier to get a full SSB5 further down the life of the system. AC fits this role, as would the revival of either Wii Sports or a Mario sports series (Strikers, please). Or it could just fall entirely on the shoulders of Balloon Fight (and continued Arms/Splatoon support) for the first few months. Depending on how early the launch of the paid subscription hits, it may be too soon to hear anything to this effect.
I'm very interested to see if there will be a solution for playing Star Fox 2 without the SNES Classic, for those who can't obtain one, but something tells me we're not going to hear about it now when announcing it may inhibit demand for the SNES Classic (as though demand could possibly fall below the constrained supply, ha).
I don't expect much (or any) redundancy with the recent indie reel. Imminent releases like SteamWorld Dig 2 and Golf Story have probably received their last push before launch. Hollow Knight's developers indicated information on the progress of the Switch port would be coming this week, but they might be running on their own PR schedule for that. Actually, they've been conspicuously absent from nearly all of Nintendo's own pushes for their indie partners all year.