I mean even though society is transphobic it still manages to produce "research" or really just any discussion at all on the subject. I couldn't find a single article or the like. I'm just used to queer identities having some sort of representation in the LGTBQ sphere, rather than just popping up on a website with seemingly no history - like neopronouns didn't just come from out of nowhere.
While you say swarmgender isn't a mental illness, you also admit that the psychiatric field has a history of cataloguing gender identities diverging from the binary. While non-binary isn't a mental illness, it was still studied enough to be in the DSM, so it's existence was known - it was just treated with bigotry.
I don't think of any specific field, but usually there is something, anything really.