Obviously MP4 was a no show at E3 and we found out last year the whole game has been started over from scratch. With the recent tweet from Retro that they are just now looking to hire for a key art director role in the game, it would seem likely they still haven't even started official development yet. Moreover, with the last five years amounting to literally nothing over at Retro, we can't assume they are at all capable of developing a top notch game in a speedy manner (if they're even capable of developing a top notch game at all these days, but that's for a different topic).

In other words, MP4 is still a long, long ways away. Like maybe up to 5 years long, but 3 at the very least. That range would put it in the same proximity as when the Switch successor will likely launch (2022 at the earliest, 2024 at the latest). It seems like a given at this point that at the very least MP4 would be another TP/BOTW dual system release. However, those games were well into development for current gen consoles when they got ported over to the next gen ones. Given it seems Retro hasn't even started development on MP4 yet, I think Nintendo may very well want the game moved to the Switch successor. While I know some might say this would create a backlash since it was originally announced as a Switch title, keep in mind that the game originally announced no longer exists. It was scrapped, everything is starting over.

Furthermore, the Switch is no Wii U situation. Nintendo had to deliver BOTW to Wii U owners given the shortage of truly AAA great games for that system. Switch on the other hand is already looking like it may amass one of the greatest software libraries of any Nintendo system ever when all is said and done. Anyone who bought a Switch based off of the 2017 MP4 announcement would be highly unlikely not to be satisfied with their purchase of the system overall because of one game not coming.

So in the end, given all these factors I think it makes a lot of sense that MP4 will be commissioned as the showcase title for the Switch successor's launch window. The Switch's place as one of the most successful consoles in history is set in stone at this point, Nintendo doesn't need MP4 for the Switch anymore. What better way to create hype for the successor than a truly next gen Metroid game with years of built up anticipation? 

I will buy MP4, and play it on whatever system it is best suited on. And it'd better support all those amiibos I've stockpiled since Smash, Federation Force, and Returns. :P

I am patient. Please make Metroid Prime 4 great again.

Next...

They are still looking for the key art director. They are clearly only in early pre-development phase, and actual development will take 2 full years at the very shortest. There's no way this is releasing before another 3 years, that would be a "normal" development time for a Nintendo project, not a long one. And 3 more years would also be a normal 5 year system cycle for Switch. Add another year because of the Switch's success and we would still almost surely see the successor in 2023. Nintendo will be well aware of this, hence why I think they would have the foresight to want the project moved to the successor. 

I think it's still coming for Switch, even if it takes another 3 or 4 years.

Handhelds are not an accurate comparison. Switch is not a handheld exclusively. No Nintendo home console has gone longer than 6 years. Nintendo won't risk releasing the successor later than 2023 and getting that behind in terms of what's being done in the industry. The Switch is going to start to feel archaic compared to what developers are doing on PS5/X4 by 2023, Nintendo will feel like they're in the dark ages if they push the Switch further than that and it will hurt their reputation. 

Thank you for opening this discussion ! I was really afraid to propose this idea here...

So to add my view, that some might not appreciate, I would say that the first base of the game was not really a failure or a disapointement, but it was decided by the highest heads of Nintendo that MP4, with every possible artistical direction and code optimisation, the game would just look ridiculous with a release on 2020 compared to the very last 8th gen games and the coming trailers and demo of the 9th gen. So they scraped it to restart with a more powerfull structure.

Or a softer hypothesis : they scraped it because they wanted a full use of the capacity of the Switch Pro coming soon.

Good point, I never thought of the idea that maybe MP4 was going well, but they just felt the Switch wasn't up to handling their vision for it so they are restarting with more powerful hardware. However, I'm not sure I can agree on the idea of a mid gen Switch upgrade that plays exclusive games the Switch doesn't. I mean, that would be pretty hard for Nintendo to successfully market and sell. One of the biggest reasons listed for Wii U's failure is that the name made it sound like an upgrade not a new system, and most people aren't going to want to buy an upgrade of a system they already have to play new games. Upgrades of systems work best as a way for tech junkies to get their fix, not by being required to play certain games. 

Have you already tried to run Ocarina of Time N64 at 60fps on an emulator, on a machine 1000 times more powerfull than a N64 ? You can't, because the game has native script limitation which just prevent it. BotW is certainly more a WiiU port to the Switch than a native Switch structure downgraded and ported to the WiiU. I totaly think they can decide to restart, like 80% of the work to rebuild the game optimaly for the Switch Pro, and then downgrad it for the base switch.

In that case it is the same thing to announce : "we restart from the begining" or : "we have to rebuild most of the game structure".

I am very superficial in hardware/software technic, so anyone here can say that I am saying bullshit, I try to stay general only as much as possible.

Not true as NES originally released in 1983 with SNES releasing originally in 1990 which is 7 years they did that because their spot in the market was good also portables are a fair comparison because as it stands now the's no real alternative in the dedicated portable market to Switch so the portable performances have to be accounted for as well. What developers do on PS5/X4 won't really affect Switch same as like what's done on PS4/X1 doesn't affect it as the Switch's library is driven by exclusive and titles that don't require heavy specs to run same reason 3DS has had a 8 year run.

I'll add being the only device in the dedicated portable market due to its hybrid form factor will dictate a lot of what happens for example Gameboy's monopoly gave it a 9 year run before the GBC model was introduced which is essentially a pro-model of sorts and the actual successor came 3 years later meaning the GB had 12 years on the market before its successor released and it was discontinued two years later so 14 years active.

Just because they're searching for an art director it doesnt mean that there was no one in those shoes (even as placeholder) and that a fair amount of development hasn't already taken place. If up until now they've been getting mechanics, script and story in place and need some fine tuning where art is concerned it could arrive in 2 years without being rushed.

And starting from scratch likely means the technical stuff (just as FFXV started from scratch) so they could already have a strong art and story basis to work from