A press release for today's surprise Sonic Lost World new Yoshi's Island level for Wii U includes the following tease, reprinted here with the original emphasis: "And get ready to link to another special DLC for Sonic Lost World in 2014. More info to come on that one shortly."
That sure looks like the tease of a Zelda-themed level. Neat!
UPDATE: I've added an image from today's Nintendo Direct that I hadn't caught when it first aired. My stream faltered. Thankfully, many of you spotted it and pointed it out. Looks like we can consider this confirmed!