Shigeru Miyamoto says that the Star Fox amiibo unlocks will be purely cosmetic.
Ever since the release of Nintendo's amiibos, fans have been concerned that they are being exploited as form of "Physical DLC," like, for instance, in [i]Splatoon[i], where a whole series of challenge maps are locked behind the amiibo wall. Thankfully, in an interview with Kotaku, Nintendo's Shigreu Miyamoto claims that this won't be the case for Star Fox Zero, and that any amiibo interaction would be purely cosmetic.
"In terms of being able to unlock content [with amiibos], I don't really want to go down that path," explained Miyamoto. "For this game, I think of it more as, for people who have the amiibo, they're going to get a little something extra and that's how I'm planning on it with this game. So rather than actual abilities or things like that changing in the game, it would be like getting a different skin for the Arwing or something like that."
"In terms of what I'm doing with Star Fox, I'm really not thinking about there being locked content or there being a mode that you won't be able to play if you don't have one. Since we already have the existing Smash Bros. amiibos I basically want to put in something so if you already have those amiibos, I imagine people will try and tap them on Star Fox anyway, and I want to make sure there is something that gives them a nice charge when they do that," he added, confirming that Star Fox Zero most likely won't have it's own unique amiibos, and will simply use the Fox and Falco Super Smash Bros. amiibos.
This is really the way that amiibos should be used - little cosmetic extras.