There's been no word in the west on when players can expect the addition content for Mario + Rabbids, but it appears Japan might have casually slipped these details out in the eShop listing. According to the to the page on the expansion pass, the story content will apparently be released on on June 30 of this year for Japan.

This isn't a set in stone confirmation for a worldwide release, but at least hints at when Japan can expect to be playing the expansion. With the date so far away the date could still easily change until we get an official confirmation, but it at least gives a clearer look at when players can look forward to hopping back into the mixed up world of Mario and Rabbids.