I'm predicting Animal Crossing at or near launch. It's been 5 years since the last one and that was an absolute phenomenon (partly because of world events, but AC is always a pretty big deal). I think Animal Crossing is much more of a system seller than most people think, and if I were Nintendo I'd try super hard to get AC out at launch.
Since the same team does both Splatoon and Animal Crossing, I think we'll get one or the other. Maybe an enhanced version of Splatoon 3 since we know those are coming now, or just some new content since it'll be backwards compatible.
Both hoping I'm right since I love Animal Crossing, and hoping I'm wrong because I've been playing a ton of Splatoon 3 lately and would love some new Salmon Run waves and bosses.
on a related note, I really hope DLSS isn't mandatory on switch 2. I tried using it in Portal: RTX and it made me really nauseous. Something about the low sample rates made the textures swirl a ton, and that was on my roommates' 3070 rig, which there's no chance of the Switch 2 having comparable performance to. Maybe if they're being super careful it could work, but I haven't been impressed with my firsthand experiences with it so far.