I'd be a little more optimistic personally. Mario Golf had it's file size already on it's eShop page when it was announced in February 2021 which is a good indicator to tell us that game wrapped base-game development much earlier and I'd assume their next project would've started development around the second half of 2020 at the latest. I think Camelot's next project will still have the Switch in mind as I don't think they would've received dev kits for the Switch successor that far back as well.
Games have their file sizes listed on the site before they go gold. Ultimate's was up two months before base development finished, which was in November 2018, only one month before it launched. Currently Pikmin 4 (the title furthest away with a date) has its file size up, and... it's possible the game is done development, but it's still five months away, so it's also very possible it isn't.
So that evidence is inadmissible.
Plus the Switch successor coming out next year is just speculation right now, there isn't much leading to that being definitively the case at this point.
It's a pretty reasonable prediction though, given the console's age.
Also I feel like a late-life game on the Switch would generally fair better in general than in the DS era. Social media is a much different beast than in 2010 and the Switch has has a more consistently high attach rate throughout it's life in comparison. I think it's fairly possible that the Switch would share an ecosystem with it's successor fairly closely since I feel Nintendo would want to hold onto the large userbase for a little while longer
I think a late-life game would fare better on the Switch than the DS too, but I also made the distinction of a game that released after the next thing is already out. Then I think we could be in trouble. I think the moment the next thing gets announced, it will impact software sales, but especially once its released.
But yeah, if Camelot's game releases this holiday, for example, and we don't learn about the next thing until next year when it releases, then I'd expect the game to still perform pretty well, despite being seven years into the Switch's life.
