About a year ago, in an earnings report, Nintendo revealed that it was working on Mario Kart Tour, the first game in the franchise to be developed for mobile devices. While not many details were provided, the title was expected sometime this fiscal year, which is to say before the end of March 2019.
Today, Nintendo released its quarterly earnings report for the third quarter of 2018, and with it came the announcement that the game has been delayed. According to the company, the title will now be arriving in the summer of 2019. The delay is meant to give the company time to improve the quality of the app and "expand the content offerings after launch".
Aside from that, there's still not much in the way of details regarding Mario Kart Tour, including whether or not the game will be paid for upfront or be supported by microtransactions. Super Mario Run was one of the first smartphone games Nintendo developed, and it cost $10 at launch. On the other hand, Nintendo's mobile IP Dragalia Lost is a free-to-play title.
Hopefully, we'll get a look at Mario Kart's debut on smartphones sooner rather than later. Until then, the best way to enjoy the franchise might be Mario Kart 8 Deluxe on the Nintendo Switch.