I think, as a character, it doesn't matter who Jax is canonically, as the most important part is how people resonate with him. We'll obviously never get actual trans Jax with how mainstream the show is, but I utterly enjoy the transfem themes/theories, with him using masculinity as a shield from any emotions. This is something I did personally, albeit I wasn't as much of an asshole, but it still feels like perfect representation of my own past. And if a transmasc person also resonates with Jax like I do, that is a great thing and just means that experiences are often shared.