I know Prime games really haven't focused on multiplayer, but I hope it's something they're seriously investing in for Prime 4. It's really a golden opportunity to bring an exclusive, AAA multiplayer FPS to the Switch. Something on the scale of what a Halo multiplayer game offers in terms of maps, features, content, etc, would be amazing.
I honestly don't thnk mulltiplayer is a fit for the Metroid franchise. Newer gamers who were only recently exposed to it through the Prime series seem to erroneously compare Metroid with Halo in terms of scope, gameplay priorities, and atmosphere. Metroid is more like the first Alien movie, whereas Halo is, at its closest,
Aliens when it introduced the Flood. Metroid focuses on isolation and exploration, as well as traversing hazardous terrain, while Halo focuses on combat/gunplay, and weapon and enemy varieties.
So no, Metroid should stay singleplayer, and should primarily focus on singleplayer. Don't waste time making a multiplayer mode like in Echoes. It's like asking for Aliens: Colonial Marines when what you really want is Alien Isolation.