Not a Nindie, but I think I stumbled upon the DLC date for the story expansion (atleast in JP) for #MarioRabbids... on the Japanese eshop listing for the expansion pass it lists this. @grantkirkhope @DavideSoliani #NintendoSwitch pic.twitter.com/RpDHUgGz8i— Switch Nindies (@SwitchIndie) January 3, 2018
While we wait for a date when it comes to Mario + Rabbids Kingdom Battle's story expansion DLC in here in the states, it looks like Japan has their answer. An eShop listing clearly shows the content releasing on June 30th, 2018. Hopefully that's the case around the whole world, if not sooner!