It does feel.. odd to be introducing this right at the end yeah. Like.. I guess it wouldn't be the first companion that pined over a doctor who then went into a regeneration but like.. I dunno.
I dunno if they even will go back to a guy for the next regen. It would be a twist on the romance part and add drama, unless shes bi, but I feel like BBC would get dragged into the firery pits of news media hell if they "went backwards" making the next doctor a dude, even if they weren't a white dude.
And yet, I can see them still doing it in an 'extreme' course correction maneuver. I'd rather it not, but if they did and kept Yaz, the above plotline would at least be something that would still keep them progressive and relatable. Its something that people can come across, they fall in love with someone who ends up realizing their transgender, and how that would effect them, if it would effect them. But only if its handled well, and RTD isn't terrible when it comes to that. I don't have 100% trust; but I never really hated his stuff (not even Last of the Time Lords).