During a roundtable interview yesterday with Yoshiaki Koizumi and Kenta Motokura of Nintendo EPD, the possibility of multiplayer in Super Mario Odyssey came up and was all but confirmed by Koizumi.
When asked about multiplayer and online support, Koizumi stated: "The first thing I want to say about multiplayer is that since this is the Nintendo Switch, and it does have two controllers, it's very easy for you to imagine handing one to another person. So there probably is some...thing you'll hear about multiplayer. The timing is not quite there, so I hope you're able to wait for a little longer to hear about that."
"As for Network features," Koizumi continued, "since this is something the hardware is capable of, there might be something that you'll head about there as well, and we hope you'll look forward to it."