I think they're hinting at a cartel war with that shooting at the opening of the episode. Gus got that cartel leader killed last season, they'll want revenge, and that would be an opportunity for Walt/Jesse to duck out of the way while everyone kills everyone...
I wouldn't be surprised if a main character or two gets killed this season, they've basically not lost anyone yet...maybe Saul
I agree, Gus is the hidden key player until now. But I haven't still understood why he killed his faithful Victor in the first episode.