I had the same thought... That since Jesse knows Sam and Dean, they are the only ones who can get through to him and help him resolve the issue. Dean Jr. knows his Dad and Uncle's relationship with God (Jack) and Jack brings them back.

Just as we learned John had a son (Adam), I'd love to hear from a daughter that also called John her father. In all those years, John never had another child? Take that and run with it - Sam and Dean meet their half sister. Maybe she's even in the life, hunting with a small crew of her own. Together they can take down some of the "ones that got away", like the Amazons.