My intuition would be the opposite. Has anyone done research on whether people in the categories you list more easily remember to use and interpret "they/them/their" as singular, or "ey/em/eir" or some other alternative?

(There's also the generic-pronoun vs. pick-your-own-pronoun issue; it seems like the latter has got to be bad for those folks regardless, because it adds extra cognitive burden compared to the generic case.)