As correctly remembered by hwrose379 in the comments, this box art was initially visible as a very small image in the original announcement (linked in the text below). It seems even more feasible, as a result, that this provisional design will be the final box art.
Mario Kart 8 is a vitally important, big-name release for the Wii U, as Nintendo will hope to see it prompt the levels of enthusiasm enjoyed by Mario Kart Wii and Mario Kart 7 on the Wii and 3DS. It's not that far away, either, with a worldwide May release confirmed.
With its arrival in a few months, it seems that some retailers are having a stab at box designs, and it's unclear whether they're being mocked up and since repeated around the web, or whether Nintendo's provided a provisional design for them to use. We're naturally cautious of retailers of which we've never heard, but will happily file this as a sensible provisional design now that Amazon France has joined in. The various European arms of Amazon are often in early with box designs and even, occasionally, product reveals.
If this provisional design does make the final cut, let us know whether you think it'll look good alongside the rest of your Wii U game boxes. It seems quite spiffy to us.