https://www.pcgamer.com/fortnite-founders-skins-are-finally-coming/

Fortnite Battle Royale is free, but Fortnite Save the World—the PvE portion that got the ball rolling last year—is not. It's available for purchase in different flavours of "Founder's Packs," which include various hero and weapon start packs, special weapons, and other such in-game loot. Back in March, Epic confirmed that Founder's Pack owners would also get some new skins, although a date hadn't been set at that time. Now it has. 

The 5.10 update doesn't have a hard date itself as far as I know, but it should be here sometime this week. That's the one with the new "compact SMG" that looks suspiciously like a P90 (a bit of trivia I know because I used to watch a lot of Stargate) and a change to "Slurp Juice," an uncomfortably Jarate-looking concoction that will restore player health and/or shields.