I think at least 20 missing bands TBA for the complete line up, and I'm afraid would be bands to play often in Wacken, to celebrate the anniversary together.
In the last 10 festivals these are the bands that have played more times:
FIVE TIMES:
1 Mambo Kurt 2004 2006 2007 2008 2009
2 Subway To Sally 2001 2003 2006 2007 2009
FOUR TIMES:
1 Amon Amarth 2002 2004 2006 2009
2 Children of Bodom 2002 2004 2006 2008
3 Die Apo. Reiter 2001 2003 2006 2007*
4 Doro 2000 2002 2004 2009
5 Gamma Ray 2000 2003 2006 2009
6 In Flames 2001 2003 2007 2009
7 Motorhead 2001 2004 2006 2009
8 Nevermore 2001 2004 2006 2009
9 Nightwish 2000 2001 2005 2008
10 Onkel Tom 2000 2002 2003 2005*
11 Overkill 2000 2001 2005 2007
12 Rage 2001 2003 2007 2009
13 Rose Tatto 2000 2002 2006 2007*
14 Saxon 2001 2004 2007 2009
15 Soilwork 2001 2003 2006 2008
16 Sonata Arctica 2001 2003 2005 2008
17 Stratovarius 2000 2003 2005 2007*
18 Suidakra 2002 2005 2006 2007
THREE TIMES:
1 Annihilator 2000 2001 2003
2 Arch Enemy 2001 2004 2006*
3 Cannibal Corpse 2002 2004 2007*
4 Destruction 2002 2004 2007*
5 Finntroll 2001 2005 2006*
6 Grave Digger 2001 2004 2007*
7 Hammerfall 2001 2005 2009
8 Holy Moses 2001 2005 2008
9 Hypocrisy 2000 2002 2004*
10 In Extremo 2002 2006 2009
11 J.B.O. 2002 2004 2007*
12 Kreator 2002 2005 2008
13 Lacuna Coil 2001 2007 2009
14 Metallium 2001 2003 2005
15 Mob Rules 2000 2002 2005
16 Napalm Death 2001 2007 2009
17 Opeth 2001 2006 2008
18 Primal Fear 2001 2003 2006
19 Primordial 2002 2005 2008
20 Sentenced 2000 2003 2005
21 Shandmaul 2004 2007 2009
22 Testament 2000 2003 2009
23 Turisas 2005 2007 2009
* = could be this year
= i would like
= i wouldn't like
but i insist, i missing a true headliner for the black metal stage