Jane Fairfax is a man.
I’m sure this will be wrong, just like 90% of my LBD theories, but hear me out here.
I was trying to unravel how they were going to tackle the secret engagement. Based on his tweets, I suspect Frank is a trust fund baby who is worried about his parents cutting him off. In the book, Frank’s aunt was going to disapprove of Jane because her family is poor/from a lower class. Although they could go that route, I don’t think it will work too well in a modern setting. Jane is a foil to Emma in that she is more accomplished/hard-working than Emma, but she lacks Emma’s social standing. A modern day Jane has probably gotten a full ride to Harvard or something, and I don’t reasonably see anyone’s parents rejecting the match.
But what if the relationship is a secret because Frank is coming to terms with his homosexuality? He thinks his aunt (mother?) will reject him, and he’s just not ready to come out, so Jane agrees to keep things secret. When he hangs around Emma, he is “playing straight.” He may even want to like Emma, if he is still struggling with his sexual orientation. Eventually Jane gets fed up with this.
This idea also has the potential for a Darcy-like reveal. I imagine Jane might be mentioned in a few episodes before he (that’s right! I’m using that pronoun!) appears on screen. They could avoid using gender specific pronouns, similar to what they did with Ricky Collins’ fiancee. And then when Jane finally appears in a video, we see he is a man, and our minds will be effectively blown. Except not, because you are reading this? This might also explain why there is not twitter account for Jane as well. It will be easiest to hide the secret if Jane keeps a low profile.
This begs the question, what to do about Jane’s name? I kind of hope it stays the same. In the book, Knightly often says that Emma should have been friends with Jane and be mindful of her situation. I think a better modern day equivalent would be to say that Jane was bullied. If you are a boy named Jane, you have a 100% chance of getting bullied.
Or they could change Jane’s name to something gender neutral. What if that is the real reason behind the George / Alex name switch? If they change both Jane and George’s names, the fandom will speculate that it is to avoid reusing names from LBD (as has already been done). So it will not be immediately apparent that Jane is gender swapped.
tl;dr You don’t need to read this because my theory is probably 100% false anyway.