Just a guess, of course this is all dependant on where software development is at, I'll throw in some 3rd party guesses too


August 2024:
Mario Kart World (next-gen MK title)
Metroid Prime 4 (cross-gen title)
Street Fighter VI
Final Fantasy VII Remake

September:
Smaller Scale New Nintendo IP (Labo VR type sequel)

October:
Legend of Zelda: Tears of the Kingdom 4K w/large new DLC Quest/Story Expansion
Resident Evil 2/3/4 Remakes

November:

Super Mario 3D Next (Odyssey 2?)
Call of Duty game

December:
Golden Sun RPG or lower end Nintendo IP franchise revival (cross-gen)

We don't know when the advice was given, but I'm going to assume it was when they pitched the idea, not when they completed the project.

I would assume Nintendo probably looked at that circa 2021 or something and told "well, by the time this game is finished it'll be 2023, and well you might as well just wait for the next system in that case". 

So they probably knew even back then that by about 2023/24 the new system would be close enough. 

Or simply that they have a better grasp than Ubisoft on how to properly push a product like Mario+Rabbids?

It’s the kind of game that capitalize on a softer release schedule and would have benefited from the post launch calendar of the future system.

But it’s Ubisoft and like any AAA publishers, they’re dependent on their returns on investment ASAP and can’t hold on finished product like Nintendo does.

I don't think Nintendo would suggest it if the next system wasn't reasonably near by, like otherwise it's kind of a dick suggestion (lol), "hold on for years and years before making another one". 

They probably saw "oh ok, so you want to release it in 2023 ... well Super Switch is (for example) 2024, why not just wait the 12-16 months" type of thing. 

I mean, if you’re looking for signs of the imminent release of the new system, be my guest.

I’m just seeing signs of Nintendo being aware of the brand appeal, while Ubisoft wasn’t.

Great game, but more dependent on the better release conditions than anything else. Even if that means holding onto it for 12-18 or even 36 months (who knows). 

Ubi should have waited.

My precition (which is mostly pure speculation) assuming the console came out that soon or in 2025 (though I think it could be even later down the line than that):

New 3D Mario - I actually think it'll be its own thing separate from Odyssey. I'm thinking maybe a Galaxy-esque game but with far bigger planets and more depth
New open-world and/or 2D Zelda
Prime 4 (to launch cross-platform with the tail end of Switch like Breath of the Wild w/ Wii U and Switch
F-Zero - yes I think Sega and/or Nintendo is finally gonna make it
Mario Kart 9 - or Wave Race as a gap-filler while Nintendo takes more time to finish Kart.
Luigi's Mansion 4

Here's what I think we will or might see, in approximate order of likelihood:

3D Mario and/or Mario Kart 9: The Switch 2 has to have something big for launch, and I think these are the leading candidates. Next year will mark seven years since Mario Odyssey and a full decade since the original release of Mario Kart 8. I think we'll get one of those releases at launch, with the other coming out within the following year. Those are the only truly big mega-blockbuster titles I think we'll see within the launch window given the recency of other mega-blockbusters in other series.

Yoshi, Donkey Kong Country, 2D Zelda, and Luigi's Mansion: It's been a while since the last mainline entries in those series as well, and I think there's a high likelihood of seeing those. The upcoming LM2 remaster could very well be there to generate interest for LM4.

Metroid Prime 4: This is obviously going to be a Switch 2 game at this point. I think it's possible we could see it within the system's first year, but that's probably a long shot given the near-total radio silence since it was first announced.

Smash 6: It's also been a while since Ultimate was released. I'm not sure how they'll move the series forward at this point, but you know it's coming. If it's not a Year 1 release, then probably Year 2.

Old IPs resurrected from their dormancy: A definite possibility, but specific guesses would be pure speculation. Fingers still crossed we'll one day get another F-Zero. Hell, I wouldn't mind seeing them bring back Star Tropics as a bright and colorful, less serious answer to series like Uncharted and Tomb Raider.

Possible ports: If the Switch 2 isn't backwards compatible (hopefully it is), we could see various big-name Switch titles get ported as well. Also, the last notable Wii U title never ported to the Switch was Wind Waker HD, and I wouldn't mind seeing that so I won't have to keep dusting off my Wii U.

New IPs: Nintendo doesn't release huge new IPs on the regular, but they could surprise us with something.

As for things I doubt will be released any time within the systems' first year, we just got new Splatoon, mainline Pokemon, and mainline Zelda, so we're not going to see new entries any time soon (though I think there's a slim chance for a Pokemon B&W remake). I'm going to concur with others who said Animal Crossing will probably come later, as it's a social game that could benefit from a larger install base.

Also, I do agree on a 2024 release date. I probably makes better business sense at this point to keep total sales high by resetting the console cycle than by trying to squeeze what they can out of an aging system with sales that, while still strong, are declining. However, Nintendo has actually projected 15 million units for this fiscal year, not 10 million. Just thought I'd clear that up for you, OP. Now, if they wait until 2025, then next fiscal year could see Switch shipments drop to 10-12M, which would rank down there with 2015-2016 and 1994-95, their worst years for hardware sales in the past 30 years. But it is most certainly not declining from 18M last FY to 10M this FY.

I’m surprised we got 1-2 Switch 2 before Arms 2. I’d really really enjoy Arms 2 as a launch title or close after. Really loved that game.

Can’t say for sure what’s Nintendo’s first party lineup for the Switch successor’s launch. My best guess would be:

- New 3D Mario: Whether it would be a sequel to Odyssey or an entirely new concept, Nintendo knows that they need a big first party title to lead the way. Zelda TOTK would already be old news by 2024 (assuming that’s the launch year) and a GOTY version of TOTK won’t really turn heads the way an entirely new Zelda would (unless TOTK somehow acts like MK8D and sells like crazy over time on the successor).
- Mario Kart 9 (or whatever the next one will be titled): MK8D has proven to be a go-to title for new consumers. Where MK9 will go remains to be seen, but Nintendo should realize that a big title like Mario Kart can’t wait too long to release in a console’s lifespan.
- Metroid Prime 4: at this point, I can see Prime 4 be a cross-Gen title. To fulfill the promise that it would come to Switch and to be that hardcore title that consumers seek during the launch of the next system. I’m not sure that, despite the hype, Prime 4 can be a system seller like BOTW, Smash, Splatoon, Animal Crossing, or Pokémon, but I can see it reach 4-5 million to be the best selling Metroid game ever, which is kinda tough for Metroid fans who’ve long wanted Metroid to be recognized as that third pillar in Nintendo’s arsenal of franchises.
- Some random new IP: We’ve seen Wii Sports, Nintendoland, and 1-2 Switch as among new IPs that launched with their respective systems (though 1-2 Switch was never bundled, funny enough). I can see Nintendo emphasize the new features of the next system with an out there title.
- A Nintendo musou title: I can see it happen. Whether it would be Xenoblade, Mario, Pokemon, or another Nintendo franchise, I can see it happen during the launch period.

Other than that, I’m not sure. Smash is hard to gauge since Ultimate just finished its DLC a couple of years ago and we’re not sure if Sakurai will come back to it or who would even take the reins of Smash after him. Zelda just got TOTK this year so expecting a big title next year is not feasible. Though a smaller Zelda title isn’t out of the question in a year or two. Pokémon may follow similar patterns when the 3DS and Switch launched, just release a title on DS and 3DS, respectively, before taking the next step onto the successor. Hopefully the Switch successor is backwards compatible so the next Pokémon won’t have to stay on Switch during the launch year. Any other IP can be on the successor. We’ll just have to find out.

My big question would be what third party devs will be on board from the jump?
The Switch had some nice smaller third party titles, indies, Mario+Rabbids, and Skyrim in 2017 with some surprises like Doom and Wolfenstein announced in the September 2017 direct. You’d think that by now, third parties would be more on board with a potential switch successor (especially Japanese devs), but I’m not sure if I should hold my breath. I would like to see games like Tales of Arise, Street Fighter VI, Tekken 8, King of Fighters XV, Final Fantasy VII Remake (if the successor can’t get XVI for one reason or another), Dragon Quest XII, etc.

It’s hard because we’ve seen the Switch be a runaway success and games like Monster Hunter Rise, Stories 2, Octopath, Triangle Strategy, Live a Live, DQXIS, Doom, and even The Witcher 3 did well on Switch even under Nintendo’s big shadow. But it took so long to see more original titles (or big titles in general), come to Switch. I get specs and power are factors, but if the rumors are true regarding the successor’s specs and DLSS, then I should expect more big titles (from last Gen to current) to be possible on Switch. But I just can’t help but think that even if the Switch successor does well, that third parties won’t bother releasing bigger titles on the system. Why did the Switch just get a Street Fighter anniversary collection after Ultra Street Fighter II? Why just a Tales of Vesperia remake? I know big Japanese third parties are focusing on the West, but the Switch has shown that you can do really well in all regions. The Switch has Japan in the palm of its hands, but I guess like some users here and other forums, some of the big Japanese third party devs don’t give a damn.

Sorry for the long post/rant.