Looks like Mario Golf: World Tour will receive paid downloadable content, that is if this snippet of info from the game’s eShop description is to be believed:
Test your skills in a gauntlet of course challenges, play with friends locally (using emoticons to cheer them on), or take on players around the world in online real-time tournaments. Discover additional paid downloadable courses and participate in special trial tournaments.
The short description has since been removed from the eShop. Is this the real deal or was it a slip up in the description? What kind of DLC courses are you interested in seeing?