Nintendo has just announced via Nintendo Direct that their new DLC for New Super Mario Bros. U, titled New Super Luigi U, will be landing this summer.
https://kotaku.com/new-super-mario-brothers-u-dlc-puts-luigi-in-the-spotli-5984218
The DLC, which stars Mario’s brother, Luigi, who can jump higher but slips off ledges easily, will feature shorter stages redesigned with replayability in mind—with a default timer of 100 seconds—although the familiar world map from the original game will still be used.