Seen a lot of people mentioning Foals, Florence and Royal Blood. I'd say Florence most likely of the three, I'd love Foals and Royal Blood but reckon they're both off to Glastonbury.
No ones mentioned Stereophonics. New album out in November and although they aren't everyone's cup of tea they have headlined 3 times previously. However it has only been 4 years (Same as Queen). Also Kaiser Chiefs released a new album, but no way would they headline.
Also, what about The Black Keys? Headlined in 2015 and haven't returned to the UK since, but again they could be more Glastonbury.
Personally, some lesser mentioned names lower on the bill I'd love to see there would be:
Hozier, Sam Fender, Razorlight, The Vaccines, Nothing But Thieves
As for headliners, any of these would be welcomed:
Foals, Royal Blood, The Black Keys, AC/DC (if the rumours are true), Queen, Catfish and the Bottlemen, FATM