YSRI = FG Central. Current runway can not be extended. A long North-South would have to be built. Once you have to do that then it has no advantages over a greenfields site.
Personally I think suggesting Wilton is a classic Sir Humphrey move. With the adjacent Sydney Water catchment area and the housing estates already in place and growing... It will provide another 2 to 3 years of solid controversy before it is quietly scrapped.