I don't speak French, but I can watch French, and this video from Nintendo France features Michel Ancel, the creator of the Rayman series of platformers. He's designed one of the levels appearing in the forthcoming Super Mario Maker.
Unfortunately, the rest of the discussion is in French, so to hear Ancel give his advice for level design, you'll need to be fluent. The French-language site Nintendo-Master.com, thanks to a rough Google translation, notes that the game will ship with 60 levels and that yes, one is Ancel's — he's not just doodling here for his own amusement.
Ancel still is with Ubisoft Montpellier (of France) but also is the co-founder of the new Wild Sheep Studio, which is at work on a fantasy game called Wild, which will be a PlayStation 4 exclusive. A launch date has not yet been given for the project.