I think Beherit, Blasphemy, Destroyer 666, Endstille, Gorgoroth, Marduk & Taake. Death metal, Deicide, Atheist, Morbid Angel, Wormed, Brodequin and Brain Drill.
Some good ones mentioned already. I'd especially like to see Beherit, Marduk, Taake, Deicide, Wormed, Brodequin, Brain Drill, Jungle Rot and Bolt Thrower. Morbid Angel were already confirmed
Others I'd like
Death metal - Internal Suffering, Enmity, Cryptopsy, Devourment, Mortician, Artery Eruption, Gorgasm, Malebogia, Remnants of Flesh, Putrid Pile, Suppuration, Repulsive Dissection, Nile, Dying Fetus, Decapitated, Vader, Yattering, Behemoth
Black metal - Gorgoroth, Abigor, Spite Extreme Wing, Deathspell Omega, Immortal, One Master, Raw Hatred, Sear Bliss, Satan's Almighty Penis (stupid name but great band), Xasthur, Leviathan, Summoning, Dark Funeral, Belphegor
I said one's I'd like, not one's actually available to play
Problem with Mortician is they use a human drummer live and their sound is quite dependent on a rusty, rickety sounding drum machine that gives them that really cold, soulless, inhuman sound. They used a drummer on their live album and it sucks.
I can't really see Beherit playing something like Wacken. Could potentially kill their image. Destroyer 666 I'm not a fan of. Gorgoroth I'm having second thoughts about, I love their first three albums, but the later stuff (both the King/Gaahl and the one Infernus album) weren't great. A good old set of Pentagram/Antichrist/Under the Sign numbers would go down a treat. Guess it would be too much to ask for Hat on vocals