But Id went back and added raytracing to Doom Eternal.
Ray tracing support in Doom Eternal was planned long before it released, they just left it to a post-launch patch because it wasn't very high on their priority list, given a lot of people buying the game wouldn't be able to use it.
More importantly, though, the only thing Doom Eternal uses RT for is reflections. The game features a lot of reflective surfaces, and it's relatively straightforward to take out the existing reflection implementation (cube maps/SSR/whatever) and replace it with RT reflections. If you're wondering why so many of the first games which supported RT only used it for reflections and shadows, it's because they're the two use-cases where it's easiest to insert into a rendering pipeline which was never designed for RT.
In Metroid Prime 4's case, it's quite clearly using the same or a very similar rendering pipeline to Metroid Prime Remastered, including baked environmental lighting. That makes a lot of sense for a game that's trying to squeeze as much as possible out of the Switch (and at 60fps, to boot), but it means swapping in a dynamic ray-traced lighting system for Switch 2 would be an
enormous amount of work. Realistically, the only two RT effects we could expect them to add for Switch 2 are reflections and shadows, for the same reasons mentioned above.
It's possible they might squeeze in some RT reflections, but I don't expect it to have anywhere near the amount of reflective surfaces as Doom Eternal does, particularly if the last scene in the trailer is an indication of the kind of settings to expect from the game. We could see some subtle use of RT reflections here and there, like Samus's suit in cut scenes, but it wouldn't be a transformative change. RT shadows are also a possibility, but if they can achieve good enough results with traditional shadow maps they might not see much of a benefit.