Why breaking Matt out of prison doesn't make sense
I'm pretty sure that by the end of Born Again S2, Matt got his license revoked as a lawyer and was arrested as a criminal for being Daredevil. The Defenders breaking him out of prison won't help his case, and I'm pretty sure this would ruin his character and his integrity.
With that being said, I therefore don't think Spider-Man will be breaking him out of prison in BND. Heck, I don't even think he will show up at all. If he does, he'll most likely stay in prison helping fight the Hand. But why would Marvel waste his cameo by just having him fight in a prison jumpsuit, they should probably just save him for the Spidey and Daredevil team-up film.
And thus, I also don't think the theory of Iron Fist disguising as Daredevil doesn't make sense either. Matt knew what he was doing when he practically showed everyone that he was Daredevil in court. He probably also knew the consequence for this, which is being arrested for being a vigilante. It also doesn't help that he unmasked himself in front of the Daredevil army during the Fisk confrontation. Everyone knows who he is already, so they might not go that route anymore.