Perhaps I'm not fully understanding your objections to the current approach from Fringe. This week's episode, for example, features a central story (the twins) which literally serves as the engine for exploring Olivia's character and
the alt-verse. Instead of the characters serving the mystery, the mystery is serving the characters and the series arc. Everything that transpires, even the conflict with the twins, in some way informs us about the bigger story ideas in the series. How is that not full-on serialization?
Like I said, it just might be a matter of me not quite understanding what you're trying to say. But to me, at least, it seems like Fringe has deliberately made every episode this season about its primary arc.