Assuming the Switch 2 releases 2025 that's only a year off from the next mainline Pokemon games.
The Switch 2 is almost certainly coming out 2024, so it will be out long before we get the next mainline Pokemon game.
There's a good possibility of a Switch successor having a Wii U launch depending on how things go.
Yeah, I don't see that happening unless Nintendo does what it did with the Wii U and attaches some weird gimmick nobody asked for to the console. I think Nintendo has learned their lesson from the Wii U how that will not work, and the Switch 2 will ultimately just be a beefier Switch, or something close to that concept. Nintendo can't go into a new console expecting it to fail, they have to commit to it's success.
and that they can meet demand.
This probably would have been a bigger issue a few years ago when the chip shortage was in full swing. Now that that has mostly settled, this probably won't be as big an issue now.
I think it's pretty reasonable to expect about a year of life-support, I don't think they've ever immediately, completely stopped publishing games for a console before even when they were in safer positions, so I don't see that changing now.
Nintendo won't immediately cutoff all support for the console. Technical support and online support will remain, and they will sell through any remaining stock. But history has shown that Nintendo themselves move on quickly in the home console space, for the most part. They did it when they went to the N64, then when they went to the Gamecube, then the Wii, then the Wii U. In all those situations, major game releases on the predecessor dried up immediately. Nintendo doesn't have the development capacity to support development for two consoles simultaneously.
Backwards compatibility will of course also effect how this all plays out. Assuming the Switch 2 is backwards compatible, it might make continuing to support the Switch make sense, since any game released on the Switch could be played on the Switch 2, thus making cross platform games an irrelevant issue. However, backwards compatibility also gives the Switch 2 a nice back catalog to work with, giving Nintendo more faith in the system being able to find a sure footing, since it already basically has a library to carry it.