Don't see Catfish ever getting bigging enough to be in contention for Glasto, I just can't see how they get any bigger than they are already with the instant regression of their music. Definitely think Royal Blood will be in for a shout, can see them headlining R&L on the back of a 3rd no. 1 album and then being in the frame for Glastonbury shortly after.
Maybe Harry Styles has an outside chance in a few years? Already has a huge fan base and seems to be rapidly winning over a new selection of people as well.