It's a textbook modern parallel runway, that is spaced far enough to enable simultaneous opposite direction traffic (eg in Brisbane, departing and arriving over the bay). You can read more about it here:
https://media.caapp.com.au/pdf/7fcbtp/8c4ba411-c5ff-44da-84bb-0ebf190bb213/Proposed Operating Modes.pdf
I really don't think so, not in the first 20 years of operations anyway.
Current stats for the "big 3"* (per month):
SYD - 27,768
MEL - 20,202
BNE - 17,708
*Moorabbin and Bankstown have more movements than MEL, and Archerfield only a few hundred short - but I've excluded these as they are mostly GA & helicopter movements
The difference between SYD and MEL is more than the total movements at CBR, about the same as CNS and only about 1,000 short of ADL. I just don't see that much traffic moving.
On the flip side, BNE is ripe for growth with no alternative jet-capable airports (MEL has AVV and MEB) and by far the best runway configuration of the three (with the terminals in the middle), very similar to LHR.
Beyond that it's not really an aviation question, it's a government policy question so your guess is as good as mine!