The most significant piece of business, not unexpected, but one with far-reaching consequences, are Lucas, Siobhan, and Brock taking out Emmet's skinhead killer. This is not so significant for Lucas and Siobhan, but it brings Brock thoroughly into the Lucas fold now - the head deputy is not likely to do anything to seriously oppose Lucas, given that they both just took the law into their own hands, along with Siobhan.
The most important piece of potential business was signaled at the very end of the last episode of Season 2. With Alex dead, who will lead the tribe? Nola certainly thinks she'll be the one, but Chayton Littlestone has other ideas. He's probably the only one who can best Lucas in a fight - sometimes - and for that reason alone, not to mention his passion and no-holds-barred drive, he'll make a worthy antagonist, not just for Lucas, but for Kai. So, once again, we'll have the tense and complex situation of Lucas and Kai having reason to be natural allies, but not quite able to do that, mainly because of Lucas.
Rabbit's absence could leave a hole in the narrative, seeing as what a dangerously worthy opponent he was. Littlestone can't take his place, so Banshee will either have to proceed with a different kind of story, or bring in a master villain currently not known to us. I'm looking forward to this season either way.