I dunno, haven't Emperor played in the middle of the day before at Wacken? I think they would accept a special guest slot and they seem well requested as a repeat
Wacken often has massive bands in the mid afternoon slot. Over the years this has included bands that could quite easily headline the festival including Motorhead, Type O Negative and Helloween. Type O played to one of the biggest crowds that I've seen at a festival.