Looking back at this, I think it was a miracle it was renewed and already with a 22 episode season, because from what I see, it just didn´t have the numbers for that, the ratings really went south, and were bad, but not as bad as Redemption.
Anyway, having said that, yep, I anticipate season 5 will be the last one, and NBC will kill it with season 5 episode 22, if they´re smart.
Doesn´t look like the show, could have more surprises with Red and Liz´s personal relationship, so that's done, the suitcase won't be able to provide much plot material, IMO:
So Red could go back into business, Cooper and Ressler will have to continue working with Red like it or not, struggling with their moral issues.
But I don't see the possibility of a new ingredient in the show, that could raise the ratings, and that could extend the show into a season 6.
My suggestion, is that Red dies, (take your pick as to how), and then Liz will inherit his business, she'll quit the FBI, and promises to continue with Red´s legacy, decides to leave baby Agnes in the care of a nanny, then decides to leave her n the care of a criminal, but asks the criminal to keep silence regarding the truth of who her real mother is, sounds familiar?
roll the credits...... hopefully this one won´t be picked up by Netflix, let it die in peace.