The news is only for Japan so far and there's no confirmation we can expect the DLC in the West. A Nintendo UK spokesperson told Joystiq, "The announcement this time was made by Mercedes-Benz Japan regarding their collaboration in Japan with Nintendo Co. Limited."
However: "As for the information relating to the distribution of the GLA kart for Mario Kart 8 outside Japan, we will be able to announce in the near future." So let's wait and see.
That kart is gonna take some getting used to, but the commercial Mercedes is using Mario in to promote the GLA may be even weirder. Check it out below the break.
Mario Kart 8 (4/2/14)