I hope they aren't going the Sopranos route of bringing in a new antagonist each season just to have him killed in the final episode of the year.
I don't think the new antagonist pattern will have much to do with the Sopranos as much as the constraints of this show, same could be said for Deadwood and Rome. Your dealing with a show based on history, at least to some degree. You can't really kill Nucky, Capone, Rothstein or the like or the show starts to go off the historical rails. So short of killing off an existing character like Van Alden, Eli, Harrow and the like you have to conjure a antagonist every season. And if you think about it who is left as a non historically important character that is in a position to challenge Nucky right now? Only guy who is close to that is Chalky.
The Sopranos had the same issues in that they didn't want to kill off any of the main crew to make sure the show had a long run, I'd argue anyway.