As many of you know Splatoon has recently gotten a major update that added two new weapon classes added to the game: the slosher and the splatiling. Now look at the amiibo that has already been released. The boy and girl inkling amiibo take the levels from the single player campaign and change the weapon to the roller or splatterscope depending on the amiibo. What if they decided to take the slosher and splatiling weapons and do the same thing as they did with the boy and girl inkling amiibos? As for the designs of the amiibos... I don't know.
The only design i can think of is the octolings, which would be in favor of the rumors of a playable octoling girl in the future! And remember the 8-bit minigame of the girl inkling in a platformer type game we saw in one of the earlier trailers?( just in case you guys don't remember... https://youtu.be/9EXKQQmm9EE?t=63 )Maybe that is one of the minigames that you get for defeating all the challenges.
This is just speculation of course, and I'd love to see what ideas you guys would have for new amiibos!
(Also this is my first thread! Hooray!!)