It may not come as any sort of surprise, but Hyrule Warriors appears to have online play according to the Japanese website. There is an online interactions box that explains what features will be available only by having an internet connection. Here is what it says:
“purchase of additional content, automatic posting of play status to Miiverse, and play special battle in adventure mode”
The first part is clearly talking about DLC, Miiverse integration is obvious, but that last part is what is really interesting. There will be a special battle in adventure mode that is online specific, likely giving us a fully online multiplayer mode. What do you think?