It looks like your current amiibo collection won’t be going to waste. Nintendo revealed that all available amiibo figures will work in Super Smash Bros. Ultimate. Along with that, Gamecube controller support is coming to the game. This is actually already possible on the Switch, but it is nice to see confirmation that those gamepads will still work.
Source: Destructoid Smash Bros. Ultimate will support all current amiibo and Gamecube controllers