They shouldn't make one until 2023-2024 at earliest. When they do, just make it Switch 2. Better hardware, a few new features, still compatible with old games and controllers, done.
Of course, it's Nintendo, so they won't do that.
Edit: also, honestly I hope they don't go 4K. 1080p is absolutely fine enough in my opinion, and by not upgrading the resolution it means you can have better graphics without nearly as much power - never mind the storage issue.