I don't believe the next platform is tied to LOZ:TotK, as it won't be a showcase for what is possible on the new hardware, and could add to some confusion. It would also mean a sense of predictability for Nintendo, which would ultimately lead to less reward in risk, complacency, lack of innovation and imagination, followed by stagnation, and ultimately, decline. There is no "copy and paste success" strategy. I'm also more convinced that 2024 is a possibility for it now - To be clear, most of the optimism I have is based on following the software, and a belief that a successor would launch later (i.e., not in 2022), allowing it to have better performance. Late 2023 at the earliest. Much depends on what happens in the Summer/E3 Season, and I find it hard to see how there would be a flurry of huge announcements before then. So, I really feel that this rules out a new platform in the first half of the calendar year, tbqh.
I don't feel we can or should understate the impact of a pandemic, which isn't over, by the way, and the reminder in the opening message of the last Direct should be a testament to that. But beyond that game, 3D Super Mario, perhaps a new Smash, or Kid Icarus/Nintendogs & Cats/returning IP, Or Nintendo World (theme park is opening, and a new entry with more attractions could be interesting), or perhaps a new IP could be showcases, and from 3rdP, DQ12 or a new Monster Hunter title. RE4R with motion controls is a nice call, but I feel we're further out than that. The rumoured RER3 title hasn't been revealed yet, and a platform hasn't been announced, either, so, perhaps that, too, is possible. If I recall correctly, the RER1 appeared first on the 3DS.
It might be fair to say 2D Super Mario is due, but I see that as more of an existing Switch title than a launch title - Wii U launched with 2D Super Mario, but while the NSMB series were hugely popular, having it 3 months after a 3DS entry didn't help. It was also the first time since Super Mario 64, where the 2D entry preceded the 3D one - the 3D one, while it has sold fewer copies than the 2D, is a bigger driver of hardware sales because it does a better job of communicating hardware capabilities. A 2D entry becomes a "must-have" once customers have bitten, but it is NOT the game which makes customers think "I want to buy a new $X00 console for this!!", so, I don't think they'll want to fall into that trap. SM3DWorld & Bowser's Fury was last year, with SM3DAllStars in late 2020, so, late 2023 or early 2024 for a new 3D Super Mario title would seem plausible; that's also accounting for the impact of the pandemic.
It appears that many of the big hitters/prospective showcases are currently supported on the existing Switch with no new entries announced/in sight. Splatoon 3, Xenoblade Chronicles 3, FE: Engage, Mario Kart 8 DX, LOZ: TotK won't show capabilities of new hardware. Pikmin 4 was announced yesterday, so, it won't be a showcase for the next platform, and the same is true for Metroid Prime 4 - the idea of them being moved to better hardware is a pure fantasy for a set of fans who so desperately want Nintendo/Metroid/Retro Studios Game to be "That Nintendo Visual Fidelity Piece" or "Nintendo Naughty Dog", and is a gross misunderstanding of what they're actually about. Very eye-rollworthy, but amusing nonetheless. Switch Sports has DLC, and it isn't clear whether there's more to come to Animal Crossing: New Horizons, or a new entry is in development. Even there, it's an evergreen title. Scarlet/Violet will likely have DLC, as Sword/Shield did. It's hard to see where the software momentum and key sales drivers are for the successor right now, and they would have to arrive sooner than later, with more of them, so as to avoid a 3DS launch window situation - this is another reason why I've been making the point about the importance of being fit for 3rdP PS5/XS titles. They would become a factor in this case, not "more XB1/PS4 ports".