I'm fully expecting it to be a cross-gen title, releasing in 2024 for both Switch and its successor, with it selling more on the successor with the big selling point being playing the entire game in VR. Just because it releases for the successor though doesn't mean they'll cancel the Switch version, as we saw with Wii U and Breath of the Wild.

Metroid isn't a very important IP in terms of attracting a wide audience; the core Nintendo fanbase are not very big fans of those types of games. It is an important IP to certain very loud fans. If Nintendo outright cancelled it, they would get incredibly bad PR by those very loud fans. Similarly, Retro is a highly overrated studio by mostly the exact same loud-Metroid fans. If Nintendo shut down Retro without proper justification, they would get similarly poor press from those loud fans.

A win-win situation is to give Retro Metroid Prime 4, see them fail with it, and then close the studio with little to no backlash. Also, top brass are not the people who created the game, they're the people that managed its production - and from what I heard of the original Metroid Prime games, it was a fairly horrendous production.

None of the Metroid Prime 2002 design team remains with Retro. None of the lead or senior artists or engineers are with Retro (or Nintendo). Six Retro studio artists and engineers (none of them leads or senior staff in the Metroid Prime era) were onboard with Retro for DKC Tropical Freeze. There are many times more former Retro devs (from the MP era) in Armature Studio (https://www.mobygames.com/company/armature-studio) than there are in Retro, and the ones there played far bigger roles in the development of Metroid Prime than anyone currently in the studio; since it is a studio containing the majority of the senior staff from the Metroid Prime dev team, while Retro currently has none of the senior staff.

You can look up their bios here: https://www.mobygames.com/game/gamecube/metroid-prime/credits

If Nintendo really wanted to give the game to the studio most familiar with Metroid Prime, they'd go out of their way to get Armature Studio to do it.

I know you don't want this to be true because you're a fan (and I admit, I'm not), but you have to question Nintendo's motivations for putting the game in Retro's hands when they clearly don't have the staff for a high-end FPS on the Switch.

First of all, I 100% admit that I don't have the list of people who are still with the company on hand, but its much higher than 6 people. I remember because a VGCHARTZ mod posted it the last time this discussion came up, I can try to find it if you want. Though if we're being honest, nothing will change your opinion. I'm not sure why you posted rebuttals to what I'm saying when I specified top brass, something you acknowledged,  unless you are just making a specification that I didn't need? I can't say I think it matters much whether the majority developers themselves are the same or not, seeing as how Armature is busy making mediocre games, something you conveniently left out. It's funny to see people constantly clamoring for new hands to takeover Nintendo, for new blood, but to see it as a negative thing for Retro. The point wasn't that Retro do have a majority of the old staff (again even said the top brass), but that there is a weird knack for believing only negative rumors regarding the studio. 

Second of all, look at the reception Retro has gotten by enlarge. Nintendo already have the ammo they need to close the studio off. Donkey Kong Country Tropical Freeze got a lot of flack for seeming unambitious to many people, and a lot of fans were disappointed that was the project Retro decided to work on. On top of that, they haven't released a new game in 5 years. There is no reason to believe Nintendo would get massive backlash for such a move. 

Third, this argument makes literally no sense. Nintendo would self sabotage and spend millions just to close a studio and release a mediocre Metroid game? Ok, lol. Companies don't spend the time and effort just as an excuse to close something. If there was a time to pull an unpopular move, it was after releasing a critically acclaimed title, to buffer the affect. Not after releasing a mediocre title in one of Nintendo's most acclaimed series. Don't get me wrong, as I said, Metroid isn't that important unfortunately and it doesn't sell units. But that's why it makes much more sense to cancel a game and studio when there isn't attention on it. Metroid fans, as rabbid as they are, would blame both Retro AND Nintendo.

And honestly I'm not really a fan of Retro. I've gotten Tropical Freeze twice, once on Wii U and once on Switch, and both times I couldn't get into it. I love Prime 1, but it's the only Prime I played for an extensive period of time. I'm also not a big Metroid fan because I simply haven't played many of them - Prime is the only one I finished, though I love the aesthetic and admire the franchise a lot. What I have a lot of confidence in is Nintendo. That's the basket I'm putting my eggs in. Retro is a means to an end, although I would love for them to be great as well simply because Nintendo could use as many good studios as they could get. But if they have gone bad, close them. 

I can appreciate that someone having an extraordinarily biased point of view doesn't mean they can't bring up great arguments. A fanboy can make them, and so can a hater. That being said, I don't think any of these are even close to good. 

I fail to see why Nintendo would want Retro Studios to fail to do a great job with Metroid Prime 4.

I don't think Nintendo has ever shut down a studio, if they didn't want Retro anymore they would sell them like they did with their ownership in Rare

At most it would be cross gen. They had every opportunity to can the WiiU version of Breath of the Wild and make it Switch exclusive, but they kept their promise and still released on the WiiU. Same with Twilight Princess on Wii and Gamecube. Nintendo has a history of such practices, and I doubt they would change that now with Prime 4.

If I were a betting man though, I would say late 2021 or spring 2022 as a Switch exclusive.  Any later and cross gen becomes more likely.  In no way would they ever can the Switch version without canceling the project all together.

They announced the scrapping of Prime 4 back in, what, January? I say it will be here by late 2021.

I literally state it in the post you’re replying to. So they can shut down the studio without controversy. It saves them money in the long run without having to put up with bad press.

Nintendo has similarly never had Shuntaro Furukawa before.

Also, they closed the Special Projects locates in the US prior to buying Retro. Much more recently they closed Project Sora.

You do have access to the lists, I provided links. You can see that none of Metroid Prime’s design team, and none of their senior or lead engineers, art, or animators are still with the studio.  I am talking about dev staff, not the corporate staff whose backgrounds are accounting and marketing and work mostly away from the site of the studio.

While the new guys might have some talent, most have few to no games to their credit. The original MP staff had Iguana Studios Turok games under their belt. There is nothing to suggest Retro would be any better at developing Metroid Prime 4 than any other studio. Retro Studios couldn’t even do DKC TF alone, they needed help. If Metroid Prime 2 and 3 were a decline from the first game, imagine what a distantly developed Metroid Prime 4 will be from an understaffed and inexperienced studio?

Additionally, Nintendo COULD hire an adequate team, as dozens of old Retro staff (including most of the leads and senior staff of Metroid Prime) work at Armature Studio.

They spend hundreds of millions on image. I don’t think a few million more to maintain a skeleton crew, and to let Retro run it’s course and close down without controversy is going to be considered a poor investment. Retro studios has essentially been a failure, the staff has been reportedly miserable and the studio itself fails to get work done. In almost the last decade they’ve released ONE game, and they needed help on it.

The writing has been on the walls for years.