the most fitting race human female
I've always assumed this.
In cannon (if and when Bioware ever releases cannon), I think it's likely that the SI will end up being a human female, perhaps the only female out of the 8 classes. My runner up race would be Zabrak though.
It's funny to hear folks try and deduce what the SI's actual race is because of what Kallig says or doesn't. say, or how it can't possibly be Twi'lek because Kallig's ghost doesn't have Lekku, etc.
I can't take credit for this; someone else posted this long ago. Are we 100% sure...
Just food for thought