I don't think there will be a spinoff, but there will be more with Hanna ;)
I'd be totally happy if it were possible to do a monogamous route and pick any girl, normally I don't really like that much freedom in games, but Hanna deserves her own dedicated route. I felt bad any time I did anything with the other girls, because it felt like a betrayal to this girl I liked a lot and couldn't pick exclusively. that or a spinoff would be awesome, but I dont wanna come across as demanding