It all seems a bit 'Pie in the sky' at the moment, and we're probably 30 years too early for any kind of Second International Airport talk for Perth.
However, if a General Aviation 'Airpark' type facility can be built, with infrastructure that helps to support and grow the long suffering General Aviation industry (from flight training to maintenance, etc), then who are we to complain?
The residents of Cunderdin and surrounds should benefit economically, and the icing on the cake would hopefully see a Widebody-capable Runway and Parking Area (and some navaids perhaps). Add that to the (near-ish) future potential for at least some freighter services, and you may see a very similar story to the relative success story of Wellcamp in QLD.
If Taxpayer funds are to be used, then personally I'd like to see Busselton, Geraldton and Kalgoorlie Airports enhanced to take multiple large jets and a greater share of General Aviation and associated support infrastructure first. If this Idea gets up though, and it helps grow the industry in any way shape or form, bring it on.