I don't know about the proposed changes - do we need to? ATM the law states that there doesn;t need to be a 50/50 division, and that 50/50 is not even the starting point. It depends on who is responsible for the residency of the child, and on the contribution each party made to the marriage.
If the parent reponsible does not pay, the Australian taxation office can deduct their payment straight from their account.
I don't know if that helps at all.