When asked on Twitter about the Chemical Brothers self confirming, Emily Eavis replied "Not that i've heard!".
http://twitter.com/matthewperry90/status/12877339106
http://twitter.com/emilyeavis/status/13058196642
She said something similar about Stevie Wonder playing, and look what happened there.
She could also be saying that she hadn't heard of them self confirming, not that they aren't playing.
I suspect they're probably playing a secret set again and will possibly use an alias such as The Dust Brothers or London Explosion Dust.
I'll let you know if I hear anything.