I don't believe for a second that they won't share every detail of their wedding planning, the proposal details and everything else from here on. This is typical Carrie speak, saying one sensible thing before doing the opposite. It's like when she was told about setting boundaries, and never understood that those could apply to herself too. Carrie interprets boundaries on social media as snapping at followers when she feels called out. The thought that she could genuinely just not share a privat detail hasn't crossed her mind. Her (or Joel) saying they won't share everything, means zero.