Also, why have amiibo used for online play?
For co-op, why not have each player choose a character, Fox, Slippy, Falco, Kat, Krystal, etc., with more more enemies on screen, so that you'll have to work harder as a team to help one another?
Have you ever played the Silkworm/SWIV (Firepower 2000) series?
Those shooter that allowed two players to play together with one player as a tank/jeep and the other player as a helicopter. The helicopter only fired straight ahead, but was able to fly over everything, while the tank had to drive and jump around and over obstacles (including things like using bridges). This sort of idea could be used in Star Fox, with with each player having their own screen or with a player having their own full screen on the Gamepad.
Ever since Star Fox 64, I've wanted to be able to play a full game from start to finish together with another player. They could have it so some levels will require the use of an Arwing when you're in space and the submarine when underwater, but for other stages on land, they should allow the player to choose weather they want to fly in an Arwing, or drive on land in a Landmaster (like the Jeep and Helicopter in Silwork/SWIV/Firepower 2000).