Here's an article about the incest "trend" on tv:
specifically Game of Thrones, Boardwalk Empire, Lost and a few other shows. Hopefully this is just a brief flirtation of this and that the writers will drop this by the end of this season's finale. It's ok with me that they just touch on it but to do anything past a brief flirtation is a mistake. It's kind of icky and really just came out of nowhere.