I'm going to be honest here. I didn't really expect Mario Kart 8 to have voice chat. Never crossed my mind, nor do I think it would enhance the online experience. That's just me, though. I can understand why some people would be upset with that feature not being present.

With that said, the official listing for Mario Kart 8 on the Wii U eShop doesn't make one mention of online chat. In the section of the page where 'game chat' would be listed for voice related activities, you'll find nothing. While not an official confirmation from Nintendo, voice support is looking very unlikely.