Speaking to Eurogamer at E3, Metroid Prime series producer Kensuke Tanabe said that due to the amount of content such a game would require, it would probably take several years to develop.
"If we started for Wii U now, it would likely take three years or so. So it would likely now be on Nintendo's NX console," he said.
"It's a long time but it would need to include a lot of content, which would take a lot of work on the development side."
Speaking with Tanabe, it was clear he had plenty of ideas for the game, including a focus on a single planet that has a time-shifting mechanic, similar to Metroid Prime 2: Echoes' single planet with dark and light variants.
"Instead of broadening it to more planets I would have one and would focus on the timeline, and being able to change that. That's one interesting idea I have in mind... but I understand many people thought that [Echoes] was too difficult."
I recommend checking out the complete Eurogamer article, dude gets it.
Also, he speaks of the 'NX console' and not just 'NX platform'. Could be just some kind of translation error or maybe he just stealth confirmed that it is indeed a console.