I rewatched the movie yesterday, and I come up with an idea for a storyform. It's maybe completly wrong, but I see some potenciality in it.
I think the OS is Manipulation > Playing a Role > Desire .
Most characters is pretending or playing a role to get something better: Ki-woo and Ki-jung pretended that they are rich university students to get the tutor jobs, Mr Kim and Mrs Kim also lied to get their jobs, Mrs Park prides herself on not being able to do domestic chores, so she acts as the lady of the house, Ki-woo and Da-hye (the daughter of the Parks) pretends that they are just studying together, the housekeeper pretends that she "eat enough food for two persons" to save her husband, the housekeeper's husband unintentionally plays the role of the ghost to get food from the refrigerator; Da-hye tells Ki-woo that her brother is faking his genius "Da-song stares at the sky, as if struck by inspiration, and that it is all an act. " etc.
I guess the OS Problem maybe Expectation: the Kims manipulates the Parks based on their expectations, and in many cases the characters's expectations makes problems.
We get the most personal point of view from Ki-woo, so I think he is the MC. I also think his conflict roots in Fixed Attitude: He becomes exceedingly attached to the lucky rock and dreams about an (unrealistically) better life.
Based on my prevoius choices in the OS, his MC Throughline would be:
Impulsive Responses > Confidence > Theory.
Honestly I am less confident in these choices... I think Kim-woo's basic problem is that he keeps optimisticaly dreaming about unrealistic scenarios until the end, and not able to accept the harsh reality. (Is it accurate as the problem of Theory or not? )
Based on the previous choices, the IC Thoughline would be: Situation > How Things are Changeing > Security > Problem: Expectation (>> Solution: Determination)
If I ask myself, who has the opposite worldview compared to Kim-woo's obsession with wealth, I would say the ex-housekeeper and her husband. They aren't particulary greedy, they just want enough security to stay alive.
On the other hand, Mr. Kim is clearly a Changed character, but I'm unsure about his influece on Kim-woo's point of view... Maybe when he tells his son that "it is best to never have a plan, since plans never work out the way one expects"?
In this case, the housekeeper's IC problem would be "having low expectations for life" and Mr Kim IC problem would be "having no expectations".
I also see the RS as the relationships beetwen the poor and the rich family, particularly Mr Park and Mr Kim employer/employee realtionship.
Activity > Doing > Experience > Expectation
Activity: The Kim family is doing varoius jobs for the Park family.
Experience: The Kims are much more experienced with the harsh realties, and much more streetsmart individuals than the Parks, who live a luxurious, but rather easy, superficial life. The Kims think that the Parks's luck and wealth is unfair.
Expectation: Mr. Park expects from the Kims to behave like skillful, effective workforces, without personal feelings, or opinions. ( He hates when one of his charges crosses the line.) Because Mr Park dehumanising behavior toward the Kims, and the lower class, Mr Kim feels humiliated, and stabs Mr Park in the end.
(PS: Sorry for my grammar!)