Nintendo Switch data-miners have delved into Super Mario Odyssey files and discovered a bunch of new unreleased costumes. These costumes are planned to be released at later dates.
According to the data-miners, these files have already been downloaded by players and have been implemented into the game but have been blocked by Nintendo servers.
We can assume that based on some of the costumes titles and descriptions that costumes such as the Santa outfit will be released at their respective times. What also could be speculated is that some of the costumes that don't have a respective event will be added in with a new mini-game or even a new kingdom, this is not confirmed as of yet but just a guess towards how Nintendo will release some of these very cool costume ideas.