Hi
JomSocial has been developed long time ago when there are only 2 genders only. This field is used in various part in core of JomSocial so when adding new gender, it would take time and as I mentioned above that I've already passed to our JS team for further consideration but there is no news on this yet.
In the mean time, you can consider to use custom field for now.
If there is update on this, I will let you know.
Regards