Flyingblind.
Yes it's nice to dream.... but... to state the obvious....
Unfortunately such programmes cost a lot of money upfront (...we all know not to ever pay for anything upfront in aviation!), and it's a lot of money to gamble on the future of the 19 seat market (though I'm not sure what the market demand for these aircraft is at the moment or what it will be like in future.)
In addition, with a lack of large airframe manufacturers/assemblers in Australia (or any experience in designing for that market), we would be up against stiff competition - since if there is any money to be made in that field, all the other manufacturer's will have planned for it! (Remember, there are people out there who are paid by the designers/manufacturers to analyse the markets for future opportunities...).