I wouldn't rush to be dismissive of this announcement. I have been aware of its development quietly going on for nigh on 2-years and this is the game changer that transforms and separates regional and metro services once and for all. Put aside all the previous silly notions and half baked schemes for airport rail links and think of a network that integrates the airport as a major transport hub with the rest of the transport network both metro wide and regionally AND interstate.
Picture in SIMPLISTIC terms a Y shaped network that runs like this, starting from Wallan which is the planned future outer limit of the Met network as an interchange with Standard gauge yes standard gauge existing reginal lines from Albury, Shepparton/Seymour diverting off the current alignment to go to the airport and then via Sunshine on a new line which may partially or fully use parts of the existing rail corridor to get to Sunshine but on their own pair of tracks. Similarly, a new line from Clarkefield area likely to be standard gauge as well from Swan Hill/Bemdigo into the airport station to merge with the new NE std gauge line and then from Sunshine on a new alignment or using parts of the rail corridor before arriving at Southern Cross (west) to a new dedicated terminal for these regional links plus on the same railway a 10 minute frequency airport rail shuttle between SX and the airport.
Added to this is the new Geelong Express Line (likely to be Standard gauge) and the substantially rebuilt Ballarat Express link (also potentially standard gauge).
Journey times for Albury, Shepparton/Seymour, Bendigo and Ballarat services plus interstate passenger trains very significantly reduced. Using either Sunshine or Southern Cross Stations it means regardless of where you live on a rail corridor in Metro Melbourne or Regional Victoria you get either a train all the way to Melbourne Airport and the City or at worst a single change at either SX or Sunshine to an airport train.
The Tarneit/wyndhamvale RRL is handed across in its entirety to Metro. The Melton (possibly even Bacchus Marsh) is all electrified Metro territory and regional trains come down their own pair of express tracks on a 4 track main from Melton to Sunshine and then join the new airport link into SX.
So that's why its a long, complex, hugely expensive project. Regional Victoria under this option becomes totally standard gauge for passenger and freight as the regional fleet is all gauge convertable. Metro network gets a huge increase in capacity for it's own growth. Then there are additional considerations like SG to Warrnambool to benefit passenger and freight as well.
It's multi billion dollars it requires very considerable detailed planning and phasing including major decisions about gauge standardization and then all that's left in the system is the Latrobe Valley and Gippsland. V/Line then basically reverts back to pure regional service provider and the outer fringe of Melbourne becomes pure Metro.
So its time to stop thinking piece by piece incrementally and develop a big picture perspective. In this same time horizon Melbourne will have outgrown Sydney in population. The sphere of influence of Melbourne as a major curfew free international airport grows even more considerably and the rail network is provided with the capacity to support that.