Has there been any consideration to a rail tunnel from near the existing parkway station to under the terminal? I know tunneling can be expensive but it would overcome many obstacles such as gradient and current infrastructure and you could use escalators similar to the underground stations. It could even be designed as a loop from the mainline giving through trains in both directions.
A loop of the main line would be the ideal solution from the airports point of view but it would have to be a non starter due to cost.
No doubt the airport will be looking for a major contribution to the building of a fixed light rail link to the airport. The fact that there has been two major statements about a link in the last few months I am now thinking it will happen, as the airport team will have egg on their faces if they now turn around and say it now wont happen.
The issue will be who will fund it, no doubt the airport will be looking for a grant which could delay the project for years. This planning of a fixed rail link has to be linked to the airport looking beyond 18 million for no other reason than they don't need it to reach 18 million passengers.