Headcanons back in the day were different. They were all about small little things that could be canon or not, like personality quirks, what type of music X character would like, or so.
I dunno when did they turn into tranny fetishism collection. But I just know they got worst with the typical tumblrinas screaming "IF YOU DON'T AGREE YOUR A RACEST WHATEVERPHOBE!!!" like spoiled little brats. I never even see "original" headcanons anymore.
Funny because there is media out there that features transsexual characters (Rent, anyone?), so they could get their representation fetish from there, but for some reason actual cannon tranny characters never get talked about in dumblr.