Metroid: Samus Returns marks the launch of not only the first true Metroid game in seven years, but also the launch of a brand new Metroid amiibo line. And according to Japanese Nintendo (via NeoGAF), now we know what these amiibo will do in the game. The answer? It looks like Nintendo and developers Mercury Steam were relatively restrained in how they decided to implement amiibo functionality.
Among the things you unlock are an Elon Reserve Tank (which gives you a special recovery ability), a Metroid 2 art gallery (which is unlocked upon completing the game anyway), Metroid Marker functionality (which tells you where the nearest Metroid is), Fusion difficulty mode, which lets you play in the Fusion suit (which you unlock upon completing the game anyway), missile reserve tank, concept art gallery (again, unlocked upon beating the game anyway), energy reserve tank, and a Sound Test mode (once again, unlocked after beating the game anyway).
So, yes- most of the good stuff is obtainable in game anyway. The other stuff admittedly sounds appealing, but also takes away a lot of the challenge from the game, it sounds like. So maybe we are better off without it. Metroid: Samus Returns launches exclusively on the Nintendo 3DS in September.