After Deb's psycho little talk about not caring about shooting the bad guy, it looks like they're definitely going for the Deb finds out angle by the end of the season, which is good, they shouldn't drag it out too much longer.
After that, the series got really weird -- right down to the whole Moloch thing. (The "Dark Passenger" is a demonic possession? REALLY?)
I kind of liked that! But if I'm watching the TV show, there's no value to me of having the books go in the same real-world direction. I'd like to see where the Moloch thing goes (though I've heard Lindsay dropped it because of the backlash).
I can see this happening: Weller's character wants to out Dexter but Quinn doesn't want to due to his relationship with Deb. He tries to stop Weller and Weller shoots him. Quinn manages to call Deb or she finds him before he dies and he warns her about Weller and reveals Dexter's secret so Deb goes after Weller to try to stop him or she goes to warn Dexter.
Sounds like a plausible scenario. I bet Lumen survives the season and drops out of the series on her own accord, without ever ratting Dex out, and with the implication that she never will. Most likely the boyfriend comes back into the picture.
Lumen's overall purpose may be to foreshadow the idea that Dexter can also drop out of the murderous life like her, with no repercussions. Lumen is less nuts than Dexter so it's an option for her. But her effect on Dexter seems to be softening him up - when he claimed to be helping her in order to stop the rapists, as opposed to the "real" reason of needing to kill, it sounded like he really believed it.
I've been a bit grumpy that Lumen isn't more of a psycho, maybe angry at all men and Dex can't see it, so that she becomes a threat to him that the audience perceives before he does. That would add an edge to their scenes. But if her purpose in the story is what I just described, then she has to be portrayed as someone who is not a threat to Dex, doesn't need to be killed at the end of the season, and can foreshadow how the writers intend to end the series.