There was an interview where they asked if every character in Smash would receive an Amiibo, and the answer was, "That's the plan." So if you expect a character to be in Smash, expect to see its Amiibo at some point, as well.If I had to prioritize - assuming literally every Smash Bros. character is getting an Amiibo - then I'd probably opt for Sonic, Mega Man, Little Mac, Captain Falcon and Shulk first. Not sure what order of those five, but they're the ones that interest me the most.
EDIT: Although I do wonder how they'll handle Mii Fighters. The three stock Miis on one circle? Or separate ones to summon specific classes?