I think Metroid Prime 4 will be cross-platform at best (at best!). It's true we don't really know much about the game, but it's probably better to assume it's due for release on the OG Switch.
Also, I have said it before but I think people overthink the issue of the console's name. While Wii U was a terrible name, the confusion wasn't solely due to it (Nintendo really botched the initial reveal and subsequent marketing), and that wasn't the primary reason why it flopped.
As long as the marketing is on point, the new "gimmick" or hardware feature of the console is not as intrusive/confusing as the Gamepad was, and the big games are there on the first six months, the Switch successor won't suffer the same fate as the Wii U even if they name it something like "Switch Advance", "Switch Magnus" or whatever.