The short answer is it won’t. The clauses in the Family Law Act relating to spousal maintenance and property division between married spouses already have corresponding clauses for de-facto couples (whether heterosexual or same-sex).
So even before the changes were made to the Marriage Act, same-sex de facto couples had the same rights in a property settlement as married couples. If a de facto same-sex couple decide to marry, their property rights at separation would be the same as if they had remained as a de facto couple.
However, it is important to note the practical difference in making an application for a de facto property settlement as compared to property settlement following the breakdown of a marriage. Separating de facto couples must establish the existence of the de facto relationship, by providing details such as the length of the relationship, the living arrangements and the contributions made to the relationship, amongst more. If there is a dispute as to whether a de facto relationship actually exists (as defined in section 4AA Family Law Act 1975), it may be necessary for a preliminary hearing to decide this preliminary question before the property settlement can be resolved.
The significant effect of the changes to the Marriage Act is that same-sex couples now have the choice whether to be married or to remain as a de facto couple, regardless of the fact that this choice will not affect their rights in a property settlement.