Metroid won't be going anywhere if Nintendo has anything to say about it. Given their attitude towards the series (and the disaster that is Federation Force), don't expect anything Metroid related for quite a while.
Federation Force was just a 3DS mistake (only sort of). One could bundle it into the just good enough for a 3DS game (which it was) and leave it there. The real issue here is Other M. That game was comically bad. I even wanted to finish i but ti got to a point in which the game was bugged and I could not progress. Basically a soft lock. That's when I gave up on the game. I only bought it for $5 so I'm not worried though.
Nintendo have the Prime Trilogy - Metroid done well and Other M - Metroid done bad.
Actually I could see another game more along the lines of Super Metroid being released. All of the primarily 2D metroid games have been pretty good. Much easier and cheaper to produce and there is a retro styled game revival currently happening. People would buy a good 2D metroid game. I would.
Metroid is an IP that'd suit an open world.
I honestly don't know. metroid as an IP is all about collecting loot to open more areas of the world, to collect even more loot and repeat the process. Taking speed run glitches out of the equation, this is a relatively linear progression. Zelda: Breath of the Wild gets away with being open world because all of the loot in other Zelda games (that foster thsi kind if game linearity) simply does not exist. The fact you can rush to the end of the game in 1 hour of BotW really proves this.
An open world Metroid game would have to deal with this somehow. You would have to have the loot simply not exist in the game or the loot would not be required to explore the game world. This is not impossible to do but you'd have to radically re-think what a Metroid game is at a core fundamental level. Nintendo did this with BotW. So it's not impossible.
I think it is possible for Metroid to go open world, but not in a BotW kind of way. It would be better handled in a Xenoblade Chronicles X kind of way. Samus can still collect all the loot she wants, it does not have to be scrapped from the game. None of the loot would be needed for exploration like in every other Metroid game. The loot would be needed to complete world objectives and quests (Like how it was to fill out the main objective in every map hexagon in XCX). This would keep the loot hunting aspect of Metroid alive but in a way that does not prevent exploration anywhere from the start of the game.