In the past the reasoning for running the New Cross branch has been that it enabled more services on the core section, but the announcement recognised that the main demand is south of New Cross Gate (actually between Brockley and Canada Water) rather than further north.

This means that the New Cross branch has little justification any longer except possibly as an easy transfer to national rail services to Lewisham and Kent.

But I doubt that TfL would reduce any services to 30 minute intervals as it goes against the grain of train planning. More likely would be the end of the New Cross branch, but I don't think they will bother as they can still run that number of trains through the central section, until there is more demand on the Peckham branch.