When news broke that Slayer was going to retire, Kerry King's wife Ayesha made things clear "don't hold your breath" regarding new Slayer music but "[Kerry] says not to worry, you’ll always get music from him." In an interview with Guitar World about his new Dean signature, when asked if we could expect Kerry to release new music after Slayer's final show, King coyly responded "Let’s just say… Dean didn’t sign me for nothing!" It looks like we have a hint of who that new music would be with.
ThePRP picked up on an interesting exchange between Slayer drummer Paul Bostaph and fellow drummer Jason Bittner of Overkill and Shadows Fall. When Bostaph posted photos of his self-imposed quarantine, Bittner asked if Bostaph had any post-Slayer projects down the pipeline?
Bostaph responded "Something is brewing with a friend of mine that is very familiar to you. I'll give you three guesses."
Bittner chimed in "Kerry [King], Gary [Holt] and [Phil] Anselmo]. C'mon, everyone knows by now."
Whether it's true or not, and if it should be said in public or not is a point of discussion. But if Bittner is accurate, that would essentially mean that King took Slayer's final lineup and since Tom Araya made it very clear he didn't want to tour anymore, got Phil Anselmo to cover vocals for him.
Blabbermouth notes that Holt has made it clear in recent interviews that he is focusing on new Exodus, thus putting into question his availability for such a project.
For now, this should be treated as a very loose rumor, but the prospect of Anselmo and King collaborating seems pretty intriguing.