I'm pessimistic. 15 million is what I think it will manage before news of the successor is unveiled, and maybe another million or two more before it is discontinued.
Having said that, Nintendo is good at surprising us with stuff - I mean, this NFC capability will have been sitting dormant for 2 years by the time Amiibos hit the shelves this holiday, and they are yet to utilise the Wii U's capability to support a second Gamepad controller. Will we see new games bundled with an extra controller in 2015? Who knows.
Even if Amiibo and any multiple Gamepad games are released, I don't think it will ever break 20 million.







