According to the new blogpost - https://www.teamfortress.com/post.php?id=189493 😻
The last few Team Fortress summer events have only been item updates. But this year, we're planning on shipping a full-on update-sized update — with items, maps, taunts, unusual effects, war paints and who knows what else?! Which means we need Steam Workshop content! YOUR Steam Workshop content!
Make sure to get your submissions into the Steam Workshop by May 1st, so they can be considered for this as-yet-unnamed, un-themed, but still very exciting summer-situated (but not summer-themed) (unless you wanted to develop summer-themed stuff) update.