THIS IS HEAVILY WORK-IN-PROGRESS.
"There is no scientific research on endogenic systems."
↳ It's true that you won't find a study on "endogenic systems", as this is a relatively new community term, and not a scientific one.
There is starting to be more research looking into non-disordered multiplicity; but most of it is being conducted by neurotypical singlets, just as research on disordered systems, and other mental abnormalities. Don't forget how you have been treated by some of these professionals (Onno van der Hart [1], Allen Francis [2, 3, 4].