They are quite reliable as they have connections to MLK (that's the organizing company). At this point of time though these bands are the ones MLK mentioned in interviews (AC / DC and The Killers for example) or which anounced they'd do festivals in Europe (AC / DC as well).
Kings of Leon and the Killers are significantly smaller in Germany than in the UK, unless they overstretch their budget with AC / DC and have to find a 'cheaper' international headliner (the Germans are usually cheaper as well, DTH don't cost nearly as much as 'Tallica or RATM) neither bands would be bigger than alternahead (which is quite something still, just look at last year's line up). Dunno how much € those bands would want at a German festival though.
About AC/DC: What really speaks against them is that they have a massive German tour planned with gigs close to RaR and RiP and said they wouldn't play pinkpop because they planned gigs in Holland already and want them to sell out. I have my fingers crossed, though.
Edited by Squig, 05 November 2008 - 01:35 PM.