Will still be available in-game
Mario Kart 8 is still alive and well in some circles (it would probably be even more prevalent if it had a good battle mode!), but online support for the TV element is winding down. On April 5, Mario Kart TV will cease its online operations entirely, and will close down at 2AM ET.
Thankfully Nintendo isn’t nixing the functionality entirely, as it will still be available within Mario Kart 8 itself. Go peruse the site now before it’s gone!
Mario Kart TV [Nintendo]