What Fortnite skins are never coming back?

I'm curious, what Fortnite skins have been permanently retired and are never coming back into the game? Have the developers released any official statements or hints about which skins might be considered too exclusive or limited-edition to ever be re-released? I'm particularly interested in knowing if any fan-favorite skins are among those that will remain a part of Fortnite's history but no longer available for players to obtain.