Wall of text below. First I want to point out that this is how I envision the next season playing out based on what I've seen. I really enjoy trying to predict how things play out on shows that I'm into.

That being said, this show is very original and will undoubtedly surprise/shock us with something we were not expecting, so literally everything that I think will happen doesn't happen at all.

To start, I think that there is going to be an event where Peter and possibly Elizabeth do something that greatly worries/angers the center, which will cause them to question the Jennings' loyalty to the cause.

The show seems to be portraying that Peter and Elizabeth are gradually going in the direction of defecting. Their work is really starting to affect them in a negative way, and there is guilt that they have inadvertently gotten Paige involved by her telling them things that Stan's son overheard and told her (which will almost undoubtedly increase in the next season).

I think that Stan will be the first to realize it's them, but he doesn't tell them about it and he starts becoming much more friendly with Peter and Elizabeth, trying to see if he can get more information on Soviet spy rings. Peter and Elizabeth suddenly get told by a worried Paige that Stan's son has blabbed that his dad is pursuing her parents, because he is in love with Paige and probably wants her out of harm's way.

Stan doesn't have a clue, and both Peter and Elizabeth realize their covers are about to be blown, and they are too afraid to reveal to the center what's happened, because they think that the KGB might just assassinate them due to whatever their massive transgression is that makes the center doubt them.

I think that things will reach a boiling point, and both Paige and Stan realize that the best option for both of them and their kids is to defect. Or maybe not, because I'm sure that Stan/the FBI/CIA suspects them for killing not only Stan's friend Chris Amador, but they have them link to many other killings as well, so they might actually reach the point that they know that they can't defect.

Either way, I really can't wait. This is such a great show, and it doesn't get nearly the recognition that it deserves.