Secret Rail plans part 3: Airport line stations lose out from East Hills overcrowding

Several blogs have speculated on the future of the Airport line, including this blog's thoughts on connecting to SRT and also Transport Sydney's similar analysis.  There is a lot of logic to connecting the Airport line to the SRT, but how does this reconcile with TfNSW's "secret rail plans" to run the Airport line instead as a shuttle to Central?  Which will it be... a shuttle to Central or a branch of SRT?  [However, for alternate views on why the Airport line should not be a branch of SRT and not also terminate at Central see this post.]

First a bit of historical background.  The Airport line was constructed in the 1990's and currently operates as a "detour" off the East Hills line, that offers an alternative route for East Hills trains to enter the city circle from the South.  Stations on this "detour" consists of Wolli creek, Domestic, International, Mascot and Green Square stations  (which I will collectively refer to as "airport stations").   As shown in the overcrowing diagram below, they are predicted to be some of the most congested parts of the entire Sydney Trains network: