That's my assumption too - Retro were simply too busy in early/mid 2017 to take on Metroid Prime 4, so Kensuke Tanabe assembled the 'new team' with Namco Bandai. My optimistic guess is in 2017 Retro dropped whatever project wasn't working and began to concentrate on Star Fox Grand Prix. We're not going to know for sure until there's a reveal, though. Shinya Takahashi's statement supports this kind of thinking, too. It's going to be a long time before we receive a Metroid Prime 4 update, which suggests that development is likely only in pre-production.

So, here is my hypothesis: After finishing Tropical Freeze, Retro went on to their next project. What that project is, we don't know. Maybe it was Starfox Grand Prix, maybe another Metroid Prime for Wii U, maybe something else entirely. After a while it became clear to Nintendo that Retro was suffering from bad management: The development went nowhere and the studio was burning through its financial resources - this is why we didn't hear from Retro for a long time. So at some point Nintendo decided to cancel Retro's game and, looking at the mess that the studio was, to give them an easier project to keep them afloat financially. This project was Tropical Freeze Switch which was released in early 2018.

There have also been rumours about Prime Trilogy Switch being basically finished and that it was supposed to be shown off last year. I suspect Nintendo let Retro do the Trilogy port: The original games were developed by Retro and it would be another easy project for them, bolstering their resources. I'll assume the rumours about Trilogy Switch being (near) finished are true and Nintendo was pleased with the result.

Then, sometimes late last year, they decided to scrap Prime 4 development as that project (developed by Bandai Namco) didn't go anywhere. Looking at Retro's good work with the ports, Nintendo decided to put the energy into restructuring / re-energising Retro. They pushed Prime Trilogy back to later in 2019 (as it wouldn't be able to function as a Prime 4 hype machine anymore) and gave Retro Prime 4 as they are the only available developer Nintendo now trusts to develop that game.

Long story short, I think Retro's "other projects" were a cancelled game, followed by Tropical Freeze Switch and Prime Trilogy Switch, as well as a period of reconstruction to get rid of the bad management at the developer and potentially to hire better stuff. I don't think there is a big new Retro game just waiting to be released. I could be wrong of course!

Going by rumours Prime 4 was being developed in an odd way where it's not one studio working the game but a few working on different aspects as a test by Nintendo to see if such a development process would yield desired results seems not, it's claimed Retro submitted a demo pitch of some project which is what made Nintendo bring them on board. Due to all the hiring at Retro and the unorthodox nature of the past few years transitioning from WiiU to NS I think they had a project they were working on which at the time was rumoured to be of sci-fi nature and it got delayed moving everything over to NS and the mass recruitment and it's possible this project may have become the pitch for Prime 4.

You can keep calling me ignorant or calling my way of thinking ''ignorance'' all you want. I'm the only one on here giving my opinion and how I think without having to try to get personal with people, so I suggest simmering down please. Its easy to have an agreement with people without trying to take it personal.  Everything I've stated, I'm standing by until MP4's release. You don't have to like it or agree with it, but just accept that thats my point of view, as I've done with yours and havent went personal on you or told you not to think the way you are thinking. For the most part your rebuttals are good and its good reading what you and others have to say in response,good conversation, but trying to take it personal, pump the breaks on that.

Maybe because she was the first person in this thread that dared to say what needed to be said and has therefore become the continuous target. i think it's cool that Retro has people that are so passionate about their work, but sadly some of us have just become disillusioned by them

I'm not making it personal. I'm just attacking your argument, and that's what a debate is all about. Personal attacks would be an ad hominem. I'm not interested in those. 

But here is the thing and you don't seem to be aware of that. I respect the opinion of others even if I don't agree with them, but your post which I've quoted first is not an opinion. What you did was stating your opinion as a fact and that's wrong. 

"They've literally done nothing but Donkey Kong games and all their ''secret'' projects never have come to fruition. They've literally done nothing. Also count the fact that nearly all the developers that worked on Prime arent' even at Retro anymore. "

You made a claim. 

https://dictionary.cambridge.org/dictionary/english/claim

And I've been calling you out on it, since a claim requires evidence or an argument that is not falling into the category of a fallacy. But your argument is made from ignorance, since, as I already stated, we don't know what RS was doing the past years. You made a claim by saying "they did literally nothing", and you need to provide evidence for this. 

Saying now that your claim is just an opinion gives me the understanding that you really don't understand the meaning of these words. 

https://www.merriam-webster.com/dictionary/opinion

https://www.dictionary.com/browse/fact

Please don't mix those up. 

And again, I am not personally attacking you. But to avoid further confusion of what you think you want to say and what you are actually saying can make a huge difference which doesn't end in your favor. Take this as a good advice.   

This thread has been so fun to read after a long weekend away from the site. So much info and opinions and just all around rambunctiousness. Man...it's going to be a very long three years as we debate so many of these ideas, and as always we'll be always wondering if this E3 is when we will see something from Retro. One thing is certain, Retro Studios will likely go down as one of the most well known and dicussed developers of all time. The next 3-4 years will cement that reputation. Now it's just a matter of seeing whether they are remembered for epic greatness or a terrible fall from grace.

I've backed up everything I've said. Even when provided with counter arguments from others, I've backed up what I have said(IE: Sports/Yankees comparison). I made a claim, people offered a rebuttal and I responded back. I fail to see the issue here. ''Take this as good advice'', Advice for what? were Just people having a conversation going back and forth on disagreements and agreements,thus is what makes good forum conversation. It seems I have gone off the grain like Melbye said and stated something unpopular to the masses, that may well be true, but that doesn't give me any less right than you to express it. 

I'm more than willing to discuss agreements and diagreements with all of you who disagree with me, I've made that abundantly clear many times, so if you wish to continue this conversation without getting heated,I'm glad to continue so we can get a better understanding of where each other are truly coming from.  If not then we should both move on to greener pastures and stop muddling up peoples conversations they wish to have with our back and forths. 

Nope that can't be it. I've never told anyone here they can't have their own argument and have actually welcomed continued discussion on the matter. Read previous statements I've made. When did having a different view and expressing a different view from the masses suddenly become ''everyone elses arguments is garbage''. If anything, aren't people taking that stance against my views currently,in which I haven't been anywhere near hostile with?