How close does DART run to the proposed Metro line? Is there any possibility of a spur on the Metro so DART users don't have to go all the way into the city to come out to the Airport again? Is there a provision for something similar to the proposed LUAS connection with DART north of Bray?
Extending the DART to the airport has some serious drawbacks. The main one is that it would require 4-tracking of the line out of Connolly to keep current services north of the airport. All stations on the line would need rebuilding, and demolition of houses adjoining the line would probably have to be done, along with serious disruption to DARTs during construction.
This would be nice to do anyway - but I don't think it would be cheaper then the Metro.