In a brand new leak from Lucas, new strings inside the Fortnite files directly hint at an upcoming Fortnite x Travis Scott collaboration. Little else is known about it, but a named set inside the file which lists all cosmetic sets is called "Travis Scott" and this implies we will be seeing Fortnite x Travis Scott cosmetics, if not also challenges, in the future.
Fortnite also included a mention to possible future concerts in v12.00 with the new 'Mute Copyrighted Emotes' setting, saying that the feature wouldn't mute event playlists such as concerts. It's unknown at the time whether a collaboration between Epic and Travis Scott will be a concert or just a cosmetic bundle like with DJ duo Major Lazer, but time will tell.
Source: Lucas7yoshi