It may just be me but... I'm not really into multiplayer games, namely because my friends aren't gamers at all (some occasionally play COD or similar games of which I'm not really a fan).
In fact, seeing you talking about a single-player campaign in Metroid Federation Force made me realize that even more. A thing noticeable about Nintendo is that many of their titles contains some multiplayer elements (Super Mario Galaxy, 3D World, Yoshi's Woolly World, etc.) where you can play the full game on your own or with friend, while others meant to be played in multiplayer (Splatoon). Nintendo seems to be aiming more and more towards multiplayer games. For what we've seen so far, Metroid Federation Force seems to be an entirely multiplayer experience. To be honest, if they do a single-player campaign, I hope they do as it is planned in the new Zelda, Tri Force Hero where in single player, the two other characters are replaced by CPUs. I might try online play to see how it works, though.
Also I wonder, if this game is centered around the Galactic Federation, could the single-player campaign be about Samus and her years in the Galactic Federation, after all the producers did say she would be in the game).