I'm going to be optimistic in terms of when we'll see the next Nintendo console and Smash game.
I think we'll see the Switch's successor in the first half of 2024. Nintendo has stated multiple times that they believe the Switch can no longer carry the sales momentum from previous years, which is a good sign that the board of directors is looking to other things long-term. Plus, the Switch's first-party line is paralleling a lot of Nintendo consoles in their twilight years. We're getting a bunch of remakes, which is how Nintendo wound the 3DS down, and a 3-D mainline Zelda, which has been the final major first-party offering in Nintendo's consoles as far as the N64. There's also the issue of Three Houses being referred to Iron17 and Engage being referred to Iron19 in their code, which would make sense if Nintendo is intentionally holding a Fire Emblem back to release as a first-party release on the Switch's successor. The Call of Duty deal also makes a lot more sense if Nintendo is releasing more powerful hardware in 2024, which gets around the issue of how a game like Modern Warfare 2 would run on the Switch's lower-end hardware.
It's also worth noting that Nintendo has never been beholden to the holiday season for releasing handhelds. The 3DS came out in February and the Switch was released in March. If Nintendo really doesn't have any more major releases throughout 2023 beyond Tears of the Kingdom, Pikmin 4, and the Scarlet/Violet DLC, they would presumably want to get the Switch's successor out early to that lost time. An early 2024 release also saves Nintendo from having to compete with the potential mid-generation upgrades to the PS5 and Xbox Series, which would almost certainly release in the holiday season.
In terms of Smash, I'm going to predict that a new Smash or a port of Ultimate will be Nintendo's big holiday 2024 title. With the exception of the 3DS, Nintendo always seems to be proactive in making sure all of their hardware has a Smash game before or within its second year on the market. Likewise, if Nintendo began work on another Smash game right as Ultimate's development concluded, that would allow them to launch Smash in October 2024 (assuming that game had a three-year like previous Smash entries). Furukawa has been clear about his belief that Nintendo's first-party software is what makes them successful, so it makes sense that'd he want an A-tier title to release in the Switch Successor's first-year holiday on market. Smash would certainly fill that role well, as Nintendo has no problem with Ultimate being their holiday title in 2018 holy **** I feel old.