what sells is stories about people's lives and their struggles that they overcome. in this context, i genuinely think the best story would be showing a person's life, starting from their childhood (which would probably put it up there in terms of PEGI), what kind of problems they have in life because of that as teenagers and adults, show where disordered life can take you and how certain unhealthy mechanisms developed, maaaaaybe show a bit of inner world as part of the struggles, but also show the healing process - resistance to it at first, a few breakthroughs that lead to opening up, struggles on the way, but the story should lead to healing and i would argue it should lead to the protagonist deciding to do final fusion, without anyone imposing it on them. It should inspire people to heal, not inspire society to change the way it operates to enable and accommodate people with a disorder. This way the spread of pseudo-did would be limited, because the message of the movie would be that aspiring to treat leads to overcoming the disorder, and live fuller, happier life. There is so little about this in DID community. Everyone just wants to be enabled for the rest of their life.
if the story would try to normalise DID plurality, it would be just propaganda for the rest of society to just start accepting it by exploiting people's compassion and empathy, which in my opinion is very selfish and wouldn't make anyone happier compared to actual healing in my opinion.