Since I've been thinking about this for a month or two and we still don't have an announcement. I figured I'd put my thoughts here.
I don't think they need to move away from the Switch. I can't see them getting anything else either. I doubt we will ever get another handheld separate from the console. Going by what they've have for the last few years with Wii and Switch and how they have developed further with a similar gimmick
My guess is the next console will be Virtual Reality based. I know someone mentioned this, but they said we would be teleported into the game and feel the pain ect, VR is not that far along. It is still a very new concept when it comes to actually doing it. And we have just recently gotten away from needing a phone. So I think it will be Nintendo Switch Reality or VR. It will come with a better type of joycon. And something for the legs. We will have the choice to play in Handheld or Console mode though. We've only gotten a few games with the straps for legs ect. VR is the only logical step they can go unless they begin following the number trend.
I think after the Mario movie, a Mario Bros game will be announced and will be the last major new game announcement not counting DLC. And then the Nintendo Switch Reality will be released in late 2025 or early 2026.
I am almost certain there will not be a Switch Pro or New Switch like people have been speculating. I think the upgraded console was the OLED regardless of what people may think.