Look on my Works, ye Mighty, and despair!
I suspect this is, in no small part, why people are generally suggesting this wouldn't happen and that, if it did, it wouldn't be a Metroid Prime.Third person Metroid Prime is no longer Metroid Prime
As noted earlier, the first-person perspective and third-person perspective should have differing strengths and weaknesses for Metroid to work with and around, meaning the different perspectives would lead to different outcomes. First-person Metroid plays differently and introduces different situations and handles situations differently than a hypothetical third-person Metroid would. This is also why development of this game is incredibly unlikely to shift to another perspective.
It's also why I really think there's room for 2D, first-person 3D, and third-person 3D to coexist in the Metroid sphere, and why I really think they should. Again, I think the best-case scenario, however unlikely it might be, would be that Nintendo is already working with another team on a third-person 3D game. And even then, third-person 3D could be realized in any number of different ways.
But, again, in my ideal scenario, Metroid Prime 4 wouldn't even be called Prime. It would start its own little arc or throughline and be given its own title for that purpose. I also think a remake of Prime: Hunters could drop the Prime title. Though I understand calling it Prime is more a marketing tool than anything.