There's no reason for calling any of his Personas "Jane".
And a new gender option would be just a new alt and voice actress. It's not fair to compare these to a full-fledged newcomer.
I did not mean to compare it to Rex as in it would take as much Dev time, I meant it as When did Atlus come up with this idea of having another Gender option for Joker and if it was Sometime in 2018 (When DLC was being Negotiated, if we don't know already) Sakurai couldn't possibly know what they would look like.
Atlus would've had to have Concept art of what she would look like, no telling if she changed or not and Atlus would've also had to share it with Sakurai to begin with in-which depending on when Joker negotiations were complete Sakurai would need to get the team to work on it and hope that Atlus didn't change the concept art. There's no telling even if they had Concept art if they met in let's say late 2017-Early 2018 as we have no Idea when the creation process of the Fem Joker was being made, Art takes time.
all these steps would've had to work out just right for this to have happened, and why would they be referred to as Jane? Cause if Brave really is Erdrick they would know at the very least that they should make the Codenames less obvious.
I have no problem with Jane if it is a Fem Joker, I welcome it but I have kind of a hard time thinking that this is super likely.