More like someone without a tour yet announced. Someone like Ariana Grande, maybe? She has a new album out, and she did headline Coachella during her last arena tour.
An optimistic take is that they are waiting for Glastonbury to make their announcement, possibly because there's a shared act that is meant to be revealed first on the Glastonbury lineup poster, which is reportedly being released next week.
Maybe St.Vincent? She has a new album coming out and she's probably going on tour, with two performances already confirmed at BottleRock and Best Kept Secret.
I'm not getting my hopes up with the Skrillex/Four Tet/Fred Again combo. Last year we had all three at Primavera and everyone was waiting for them to perform together but it never happened unfortunately.