DL is going to sell ok but not exactly going to sell amazingly, most of those bands have either just done UK tours, play the fest regularly or in the case of JP and FNM rare. Unless that is the cream of the crop of European bands playing next year then Soni could compete I think.
Off the top of my head:
Twisted Sister, ZZ Top, Accept, Venom, Exodus, Korn, In Flames, Nightwish, NOFX, Satyricon, Terror, Snot, InMe, Alice Cooper
^ not currently playing any UK fest, are around at the time, put up a couple of headliners and it could give DL a good run for their money.
Obviously Soni might not be able to get headliners, those bands didn't want to play, are committed/unannounced for other fests or whatever. But I think Soni could come back next year if only because DL isn't exactly breaking that market.
Oh joy another game of truth or troll
Your/You're, it's all the same to me