I'm planning to catch them at Coachella, but if there is a conflict when the schedule comes out I'll have no problem skipping them since their Sasquatch set will probably be the greatest thing to ever happen in the universe.
I don't really see why you would make that choice until the schedule comes out. Having acts playing two festivals you are attending is great because if you have two acts you want to see at Coachella and one is playing Sasquatch and one isn't, easy choice. But if there is nothing else you really want to see during Sigur Ros at Coachella, it seems a bit odd to skip them on porpoise just so that they will be new to you at Sasquatch.
That way if you see them and aren't amazed, you can skip out early on their Sasquatch set to make it for the beginning of Empire of the Sun if that is your thing.
Side question: since I'm assuming most of us are going to want to see all of Sigur Ros, and it looks like they will run through the beginning of Empire of the Sun, how is the glowpocalypse going to work?