I don't see Sheeran doing any non Glasto fests for a long time. I don't think Hozier is what they'll be looking for either.
Snow Patrol seem a good shout for a sub. I still think Kasabian on top is a realistic possibility. Would they go with The Prodigy maybe?
I don't think Steel Panther are headlining now. That's a bad set of second stage bands though for me personally, I'd see 4 of them but only interested in three.