Hmmm... So sometimes system can get triggered by seeing depictions of DID but also, given that DID is a trauma based disorder and things like family systems therapy work so damn well for singular people too, I think that your premise is interesting. For ethical publication, maybe add an author's note or an introduction that explains that this content is a fantasy but that it does take inspiration from a real condition, maybe add some resource information and explain that this content may be triggering for some people and that it's okay to disengage and maybe discourage people from making it an assigned reading.

I think that a world where many people are systems is way less offensive than the movies where a highly dangerous person is shown having DID. Things like subjective experiences if possession, gender fluidity, Internal Family Systems, rapid life changes, OSDD, the idea of helping spirits etc all exist. Dissassocation is a major part of human psychology and people with DID just have an extreme verison of it. Non clinical plurality can also potentially exist but that can cause internet fighting that can deeply upset a lot of people. (It is an important topic to respectfully explore but not on this thread, that's not me/my circumstances) So a world where half the people are systems makes vastly more sense than a world where only deeply criminal people are systems.