I'm no apologist for the Victorian Government but at least they are doing something. It's infrastructure and it's a bit like the desal plant. Right now everyone whinges and bitches about it but the next time there's a prolonged drought the guy who pushed it through will be considered a visionary genius. So too with railway lines. People are always going to squibble over the placement of stations and the like and it's inconvenient while they're being built but once they are up and running, it's like, "oh, this is quite handy".
The airport link in particular is a good idea. I use Tullamarine on a weekly basis and there's enough inbound and outbound pax to sustain fast and frequent trains into the CBD. Running the line through Sunshine and Footscray is the obvious idea. The key words here are fast, frequent and price competitive. Few people will pay fifteen bucks one way for a forty five minute run into the CBD with the next train in 25 minutes. Taxi ..... Run it every ten minutes, keep travel time under thirty minutes and ten bucks and the Government is probably on a winner. Keeping it as a normal zone 2(????) station would be even better.
Sydney's airport line is an example to follow on most points. It's fast, frequent, and well integrated into the wider network. Where it falls down is on price gouging. The station access fee at the domestic and international terminals is ridiculous. It's something the Victorian Government should take care to avoid. It deters patronage and ultimately, I think, adversely affects long term revenue.