Paragon's proposal has been in the news just recently, but it has been around for a while. If and when Mel gets another huge international airport it is bound to have a huge impact on investments. Here is an earlier article to start with and the latest right here.
I suggest it will happen in due time, but our govt will take a fair while to decide even if it is fully privately financed, because the govt has to create an infrastructure plan and it has to fit in with competing interests and existing financial commitments. Meanwhile it's smart to watch the news and the property market or for early birds to consider to buy. Farmland acreage in this area appears may be in limited supply once the discussion heats up. Here is the current search result for farmland in Koo Wee Rup.