What would a non-binary tā （他／她） look like?
The best candidate for a non-binary TA is in fact 他. This is particularly obvious in the word 他們 (them), which definitely does not refer to a group of specifically males. 他 did not acquire the specific meaning he until well after 她 was invented, and 他 originally was a generic word meaning other (e.g. 他人 the other person).

她 did not actually exist before the new culture movement; its creation was from the direct influence from European languages. This is commonly seen in older popular novels like Dream of the Red Chamber, where 她 makes no appearances and it is incorrect to assume that 他 means he or him.

Note: In Taiwan, 他 is still sometimes used to refer to both he/him and she/her, although this practice is declining.