...seems to be on display from the proponents of this proposal:
http://www.abc.net.au/news/2017-01-29/sa-airport-o...
Unless they're proposing to build tens of kilometres of tunnels, to avoid routes from the east going through even more suburbs than they do now, they'd have to come in from the northeast (and Monarto to Outer Harbor via Gawler is, shall we say, a somewhat indirect route - although if you were starting from scratch you'd probably bring the main rail line in from that direction).
Still, in the post-truth (or is that now "alternative facts"?) universe, it doesn't seem to matter whether your grandiose promises are actually practical or not.