A non-exhaustive list of things anti-endos/sysmeds may fakeclaim another plural for. These are all things that can apply to disordered plurals. And all things I have either heard or witnessed happening.
being under 18
having a small member count
having a large member count
having subsystems
having sidesystems
being pro endo
being endo neutral
having other disorders
being physically disabled
being trans
using neopronouns
having lots of littles
having no littles
having animal headmates
having therian/otherkin headmates
having introjects
having a core
having no core
enjoying being plural
having a period of questioning plurality
not being abused as a child
being undiagnosed
refusing to share proof of diagnosis
having headmates be primarily one gender
having headmates that are not the body's gender
using discord
headmates having exotrauma
not having an innerworld
having a vivid innerworld