I'm just a novel reader who can't access the latest online novel information. According to my knowledge, the latest book in the Monster Master series will be published in December 2022. I suggest you go to the relevant online novel platform or bookstore to inquire.
The significance of the back story in 'Back to December' lies in its ability to connect with the audience on an emotional level. It's not just a fictional tale but something that could have been based on real emotions. The idea of going back to a specific time (December) to fix things is something many people can identify with. It also helps to explain the tone of the song, which is one of melancholy and regret. Taylor Swift's sharing of this back story, whether completely true or somewhat fictionalized, makes the song more poignant and memorable.
In 'Back to December', the back story is related to a relationship that has ended. Taylor Swift uses the month of December as a symbol in the song. It could be that in December there were events that led to the end of the relationship or that December was a time when she realized her mistakes. The song's lyrics suggest that she is reflecting on her own behavior in the relationship and is sorry for how things turned out. She wants to go back to that time, perhaps to change the outcome or at least to apologize for her actions.
I haven't heard anything definite. Maybe there's a chance, but it could also be that the story has reached a natural conclusion. We'll have to keep an eye out for official announcements.
I'm not sure. It could go either way. Sometimes characters come back in unexpected ways in manga. Maybe there'll be a twist that brings Gojo back into the story.