SPN usually doesn't just leave loose narrative ends. Like, the issue/question might be resolved subtextually, textually, etc, and it might take a while, but they do eventually come back to everything. Full circle. Dean and Sam have pondered life with someone "in the life." Dean has pondered "experiencing things differently." We have the love and love thing, we have he's in love with humanity, we have Cas textually saying i love you. I gotta wonder where it's all going. What full circle is.