Third-person would definitely be worth a try. In that perspective, it would be tempting to give it to Capcom. If they get a big enough budget, I bet they would do an excellent job!
Most realistically though, Retro Studios will remain the developer, the game will be named Metroid Prime 5 (most likely with a subtitle), and it will once again be a first-person action-adventure in the vein of its predecessors. Although, they will most probably modernize it cautiously so it feels less like a GameCube game.
Honestly, I still trust Retro Studios. If you think about it, taking over the Metroid Prime 4 project and facing all kinds of troubles, I think they still did an amazing job, all things considered.
Retro Studios working on Metroid Prime 5 right from the beginning + Switch 2 exclusive (meaning they can use its full power) + Yoshio Sakamoto retired (as I feel he became a burden for the Metroid Prime series) = an excellent premise, in my opinion.
However, Retro Studios really should stick to the first-person perspective as this is their expertise; they know how to handle it. Third-person would be risky for them since they have no experience with it.
If Metroid Prime 5 stays in first-person, then I don't want Nintendo Japan (or any Japanese developer) to make it. Japanese developers aren't great at handling the first-person perspective. Motion sickness is more common in Japan, so they have a natural aversion to it.
For a first-person game, you need an American developer. They have proven that it's their turf. Even European developers haven't brought any truly memorable first-person games to the table!
Unfortunately, Metroid is a niche franchise, so the focus has to stay on the one 2D and one 3D series. Otherwise, it would be interesting if Nintendo started another spin-off series in a 3D third-person perspective. As mentioned above, that sub-series could be handed over to Capcom.