According to a recent newsletter from Nintendo of Spain, Mario Kart 8 is slated for release in April of 2014, at least for the European region. If true, this would fall along with Nintendo’s promised launch of Spring of 2014. Mario Kart Wii was released in April of 2008 worldwide, so it’s very likely that this April date is the real deal.
The tidbit comes from Twitter user DeSero who took a screenshot of the newsletter. We have not been able to track down the newsletter itself anywhere else online, so take this information, as likely true as it is, with a grain of salt. If you do have access to the newsletter, let us know!