At an ADFA open day a few years ago, I had a long discussion with a senior RAN submariner.
He hinted they already spend a lot of time cruising around in the South China sea itself - shallow water.
The supposed rationale for diesel electric boats was primarily that they are quieter and smaller than nuclear boats.
The current quietest sub in the world is Swedish and diesel/electric.
I suspect that in the classified world - the capability of long range UUVs is getting to the point that nuclear mother boat will be able to sit in deeper water for months and dispatch loyal seamen (tee hee) to sneak in and do the ultra quiet shallow water stuff.
I wonder whether the RAN will get off the shelf Virginia class boats, or the Astute class and what the weapon load out will be.