There’s likely going to be an announcement shortly, right?
The Nintendo Today app has been putting out two pieces of Metroid-related content every day for the last few days.
We know Mercury Steam are working on two titles, we just don’t know what they are, but considering their history with the franchise it’s reasonable to guess one of them is a 2D Metroid.
There’s also been a lot of whisperings of a Super Metroid remake (though I don’t buy too much into leaks unless they’re from Nate the Hate). I know it feels a bit soon after Prime 4, but Nintendo did previously release two Metroid games on the same day (Prime and Fusion), so who knows how much they really care about cannibalising that market share.