I don't think your boyfriend is bringing up engagement rings because you don't have anything else to talk about. His mind is clearly on the future.
If you consider your boyfriend the smart and empathetic type, you can assume that he's asking you these questions since he might be considering asking you a very serious question in the next few months. The reason why I say that is because a smart and empathetic guy would understand that asking you about your engagement ring preferences would give you the impression that a very important questions is imminent. As such, he wouldn't ask you about jewelry and then leave you waiting for a year.
If your boyfriend is a bit more dim-witted and doesn't understand that a woman will interpret "engagement ring talk" as "an engagement may happen soon," then you might be in for a longer wait. He's interested and probably making plans, but he didn't realize that this would trigger your "OMG MARRIAGE" radar.
Either way, congratulations in advance!