Not all that surprising, to be honest. Since the inception of Super Smash Bros. 4, Amiibos have been made into miniature figurines of our favorite video game heroes (and villains) and sold like hotcakes. Nintendo would inevitably have realized the convenience of basing a game entirely on items that are essentially collectibles. If these items make it to the market, then people will undoubtedly buy them, regardless of the price tag. Gimmicks or not, this is a judicious move on Nintendo's part, although Amiibos are hardly the only products to do this.
Making a game reliant on overpriced, gimmicky figures that are next to impossible to find half of the time is a terrible business strategy. It's bad enough that some content on existing games is functionally locked behind a paywall, but requiring you to drop sixty bucks on a game plus another twenty apiece for gimmicks?
Sadly, in this day and time it seems that the "pay-to-play" market is becoming more rampant. Given the large success of the likes of Skylanders and what I guess is the semi-success of Disney Infinity, other manufacturers distributing their products to imitate said success wouldn't be unheard of. "Amiibo World" would probably take place in a crossover universe similar to Smash Bros. in concept, but totally different in gameplay. Yeah, this endeavor would rely entirely on the appeal of, say, Kirby fighting Donkey Kong in an open-world setting, using the figures as a selling point like DisInf does. That's how I conceive their approach, anyhow.
Overall, I don't like the idea of making a game based on statues which are, again, overpriced and often hard to find. Nintendo would benefit more by making them digitally available whether in-game or through the eShop. Online purchases of the real deal tend to take several days to arrive and in-store products can sell out quickly at any time.