Stardew Valley creator Eric Barone is open to it. Per a statement given to IGN:

One time we were playing and someone said ‘what if there was a Pam skin in Fortnite?’ And it kind of became a meme for us, like we were imagining us all playing as a squad with identical Pam skins. It was just a silly fun idea.

Then someone asked me if I would collab with Fortnite and I mentioned the Pam thing. There’s nothing official in the works or anything like that, but yea we would find it amusing and fun if we were able to play as Pam (or any other Stardew character, really) someday.

Epic Games spokesperson Alex Fong declined to comment.

Update: Epic declined to comment.