Here's one I could actually see. I was at SS 09 and this years, and although I had a great time each year, the organizers should really try to make this tour more diverse, and not just focus on tech death and deathcore.
Morbid Angel - could definitely see them headlining this
The Faceless - not a huge fan but I've enjoyed them each time I've seen them, and they draw a good crowd
Immortal - not really into, but SS 09 actually had a black metal band, which would help make this more diverse
Gojira - awesome band, I saw them headline and they could easily draw 200 people or so
Rotting Christ - great and different band from previous tours
Dying Fetus - had the craziest crowd in 09
Decrepit Birth - seem to be more popular and are a good band for SS
Annotations Of An Autopsy - core band, good to draw people in
Mortician - some people would like this, idk, I can't think of anyone else. I guess they're different enough.
4/1 - Gary Numan
4/15 - Godflesh
4/23 - The Knife
4/26 - Possessed
5/16 - Slayer