One of my favorite sci fi authors, Jo Walton, had a book called Poor Relations which was very close to publication (even had cover art already) that was pulled and will never be published. It is a future sci fi but in a Dickensian class system, that involved the two main male characters becoming female under family pressure. Based on her other books, I think Walton would have handled this with intelligence and grace, but I can see why forced gender change is controversial and potentially dangerous territory to wade into and made the publisher nervous.