The most probable option is currently Maneskin / Queens of Stone Age / The Strokes, QoTSA option would be pretty weak though. Pearl Jam would be nice but they are "too old" for current Sziget crowd. Thats why Im thinking Maneskin could be announced.
And my Keane story is that I was friends with and in a very short lived band with their current guitarist Jesse in Bristol in 2000- 2001. He is a really nice guy and massively talented musician. I know after I moved away from Bristol he was a session and touring musician for loads of bands before joining Keane full time. But yeah, they've had a guitarist for ages. But it is always a reminder to me that just because you don't dig a band's music doesn't mean the people in it aren't nice people (or massively talented).