This is all pure speculation based on the idea that someone wants to use lacey in porn.
I'll note that this is a character potentially unknown to the protagonists. Why would MC be interested in this? Or Mia, who has problems with men due to childhood trauma. Anna is generally only interested in the MC. I won't mention lacey, because for me, her story is already over; in the future, she's just a bad trigger for MC's actions.
It's a huge stretch to assume blackmail is possible, but filming porn carries a stigma no less than a prison sentence, and it's 99% certain that the protagonists would rather go to the police than agree to blackmail.
However, 1% remains if we assume the complete stupidity of the MC or an unexpectedly idiotic plot twist.
Well for the MC, once he has been suitably corrupted, the reason he might support Lacey doing porn is because it would allow for Lacey to be slutty in a controlled environment, no bars or clubs, reduce the risks of her trying to find a random hook up for sex and causing problems, her partners would be professionals that would be able to keep sex and personal relationship separate so it would better, it would assure him there is a form of control over Lacey's actions so she can't do anything stupid.
As for Mia... wait did you miss what she did in College? People call her 'the Pimp' around here, why do you think that? No matter how supposedly traumatized she was with men, she had no issues effectively setting Lacey up for sex with men. As for Anna as I said she wouldn't be directly involved maybe more like an assistant to the MC after he get involved, so not doing actual porn herself.
As for the notion doing porn is equal in stigma to a prison sentence, wow, you have to come from somewhere pretty darn conservative, this is the 21st century, have you payed attention to the world around you? Their is what amount to softcore porn on Twitch and massive websites dedicated to porn, webcams left and right, and you think its still that problematic? Nah, sure its not glamorous a job, sure it won't give whoever act in it a great reputation, but it won't give them a bad reputation either.
As for blackmail, I didn't mention anything about that coming up due to blackmail, the scenario I was elaborating is basically Act 6, after they beat the bad guys they could get their hands on assets the bad guys possessed for xyz reasons and turn it into a porn studio on the Slut Path, or after all is said and done and discovering the bad guys wanted to turn Lacey into a porn actress she'll figure it might help making things 'better' and convince the group to actually do it themselves.
It depends... the fact that something happens doesn't mean it is what the MC wanted or even the result Lacey intended.
Lacey's intent is simply that she loves the MC, this however does not mean her actions will result in such that is good or healthy for the MC. Remember how she commented about how the JD backfired? How the cuck incident didn't go as she intended?
It is entirely possible that the MC gets pushed into yet another "experiment" where Lacey thinks she is "fixing" things when she is only making it worse, after all... that is typical Lacey and we have another "train wreck".
I think that falls well within the story, but what I think falls outside of it is "out of character" intent (porn empire, Lacey malicious intent, MC becoming accepting of all the behavior, etc...) which for the most part, barring inconsistencies have been pretty well established.
So while I predict more "train wrecks" and seriously stupid choices by everyone involved, I don't think (and hope) we don't see major character changes unless it is individual character growth (realization, personal growth, taking responsibility, etc...).
In the end though, who knows... everything could go upside down, but I don't think the current story supports some of the drastic predictions, those will have to have a bit more "foreshadowing" to gain any real traction.
Again I wouldn't say Lacey wanting to do porn would be out of character, it might be out of character on the Non-Slut Paths for the MC to accept, but on the Slut Path? Where Lacey has corrupted the MC into accepting her getting involved with other men? I really don't see what is so unbelievable in that. She already convinced the MC to let her cuck him, she convinced him again to let her be intimate with another man, she convinced him that her having sex with others 'don't matter', and you keep thinking she could convince him into her doing porn?
As for Lacey being malicious, I never said that, what I said is she is a slut, and she is trying to corrupt the MC into becoming sexually open and flexible, its not malicious, she doesn't want to harm him, she just want to put him in a position where he'll accept her being promiscuous and having sex with others, not out of desire to hurt him, but basically selfishness, something she has shown repeatedly to be full to the brim with. She likely truly believe that it would be to both their benefits to reach that point as it would allow her to have the sex life she want, while it would liberate the MC from his jealousy, and anxiety at the idea he could lose her.
Okay, but we get the whole drama thing... can't we move on to something else?
There are so many plot holes to fill without necessarily resorting to NTR tropes, and besides, Act 2 shows us that Lacey wants to be a better person, so...
Lacey might want to be a better person, but what does that even mean? Stop being such a narcissist, sure, maybe let go of her selfishness, sure, but it doesn't mean she wants to change her sexual proclivity, also again what we have seen up to now isn't her trying to change so much as her trying to change the MC, if you were to draw a line between the two and mark how come each have come to a middle ground, you'll notice the MC was forced to make massive headways while she hardly bulged, she said she wants to be better, but again hasn't acted on herself to change it, rather it seem she has pulled the MC to close the distance, that could be qualified as making things better, since it will help the two getting more attuned, but its done largely on the back of the MC.