I think this will launch with Zelda: TotK next May and it is a successor hardware, but Nintendo won't be migrating from the current Switch ecosystem any time soon. It'll just get the same Nintendo Switch games from Nintendo but in 4K maybe with some added effects (ray tracing or better lighting).
They likely ordered development on this chip years ago, like 2019 if not sooner, so it's simply finished or close to finished.
It'll be $399.99 minimum too I think, since I don't think the OG Switch is going anywhere, this will initially just be more like an additive model so it won't have the responsibility of having to carry an entire product line at first.
Probably a bunch of 3rd party exclusives though like Street Fighter VI and RE4 Remake and FF7 Remake I can see being announced for it.