Yeah I feel like they are nailed on for next year, probably close the festival on Sunday again.
Though if that chance arises to bring them forward a year, while demand for them is so high, would be daft not to explore it IMO. Probably not viable financially though. Would be enough for me to buy a Saturday day ticket though with them and The Killers.
I'd bet on one of Pulp or Royal Blood. Not sure if The Strokes are a festival exclusive at APE, would be another huge booking but again, would cost £££.