The polls close in a few weeks

The survey conducted by The Australian Bureau of Statistics (ABS) on same sex marriage closes in a few weeks. Today (Tuesday) the ABS announced that so far 57.5% of registered respondents have returned their survey answers. This is a voluntary survey that asks one question
The registered respondents are people enrolled to vote in Australian state and federal elections. In Australia voting in state and federal elections is compulsory - like jury duty is compulsory - but it is not compulsory to be enrolled as an elector. Most people do in fact enroll to vote and at a typical Federal election 94% or so of enrolled voters turn up to vote. Local government elections - for city councils and the like - are voluntary and usually only get about 30% participation.

I am wondering how many people will send in their answer to the survey question.