ISIS and/or Mastodon
Many people will probably disagree but considering many of you have not listened to ISIS, let alone Mastodon, I will take your thoughts with a grain of salt.
ISIS opened up for Tool during a string of US dates a few months back and they were simply amazing. Having already seen Tool three previous times, I would have paid $45 to see ISIS alone that particular night. Give their latest album, In the Absence of Truth, a listen. You will not regret it.
Mastodon is a far stretch for Coachella, I realize. Yes, this is not the Warped Tour and I know that having been to both. Let us not fool ourselves though, how many indie acts such as "The Plurals" can GV regurgitate? No, The Plurals is not a real band; at least I do not think it is. However, every time I turn my head it is The Somethings and they sound The Same. Having one or two hard acts will not turn Coachella into anarchy.