Jumping out of semi-lurker mode to say my two cents.
I have no issue if Marten and Claire end up in a relationship. But in terms of good character development, I really really hope Marten doesn't say something like "I just never thought about dating someone trans before!"
I mean, seriously, dude has a gay father. Not to mention a mom who's a professional dom and fetish model, which meant he was raised in a family where heteronormative, vanilla sexuality was not to be expected. Even if he ultimately reacted by being pretty sexually conventional, he must have went through a period he questioned it. Not in a terrified to not be straight manner, but in a "Hrrm...what's the right thing me?" manner. Thus I'd expect that every possibility, including dating someone trans, has at least crossed his mind before, even if he even ultimately rejected it.
The bottom line is I'd expect he'll either be cool with it and act as if it's no big deal (because he's actually into the idea) or he'll let her down gently. But I don't expect a lot of "huh buh wuh?" beyond Martin's typical reaction whenever a lady likes him.