Spinelli is going to be Olivia and Sonny's son. Kate and Olivia stressed many times about the fact that 25 years ago there was a big blow-up and Connie left town. If Olivia was preggers then, their son would be about 24 years old, which is Spinelli's age. He even kind of resembles Kate, who is a Falconeri. He was raised by his grandmother with never a mention about parents. That would give him family on the show. Jason raising Sonny's son would heal the rift between them. It makes sense.