It's not as clear cut as I first reckoned. They're a very strong sub, no doubt, but an out and out copper-bottomed no-qualms headliner? Not so sure. Given that the demographic of Glastonbury skews towards that vintage, they might just swing it, but it's far from a guaranteed banker. Can see it being a bit of a damp squib amongst the wider attendees.
The fans that like them, properly love them, but there are large swathes of people utterly indifferent/unaware of them, or who only know one song. Not sure I'd take the risk were I booking the festival.