Six months after my post, Parramatta city council has released a transport study. The link to this study is at:
https://www.cityofparramatta.nsw.gov.au/sites/council/files/inline-files/Att_01%20Parramatta%20CBD%20Strategic%20Transport%20Study.PDF
This study was commissioned by the local government council but used the TfNSW Strategic Transport Model (STM). It is full of reams of new data but of particular relevance is Action 10.2 on page 33, which states the following:
Action 10.2: Consider the need for, and
plan for a second railway station in the
CBD in order to offer additional travel
options from broader areas to the CBD
and address future level of demand.
Current forecasts indicate similar station
demand to Wynyard by 2036; there is a
need to decentralise demand and de-
congest the Parramatta Transport
Interchange