Nothing to major but some minor fixes to help things out. Check out the full rundown below.

Version 5.3.1 U, available via an Internet connection, includes the following improvements:
Mario Kart 8 highlight reel upload fix:

Resolved an issue that resulted in some users receiving error code 104-1852 while uploading a Mario Kart 8 highlight reel to YouTube
Improvements to system stability and usability:

Further improvements to overall system stability and other minor adjustments have been made to enhance the user experience

Link