Initially I thought it would be very similar to the SSM vote, but the more I think about it, the more I see there are key differences, namely:
- SSM was very simplistic, straightforward and easy for people to understand (i.e. can people of the same sex get married). It literally involved changing a few words in an act of parliament. The Voice referendum is more complex and abstract, it's harder for the average voter to know exactly what it is and why it is needed.
- SSM was asking for one group to receive the same rights as another. The Voice is essentially giving one group of people a special body not available to others
- The No campaign for SSM really lacked a strong, cutting argument. Most arguments essentially revolved around tradition and traditional values. The No campaign could not show how a Yes vote would have any impact to the average, heterosexual person. They tried saying "If we approve SSM, boys will start wearing dresses in school" and other stuff, but the link between the two was tenuous at best in the minds of voters. The No campaign for the Voice is really cutting through by hammering the lack of detail and how said lack of detail can lead to unintended consequences
I think this referendum is much more similar to the Republic Referendum, which lost not due to strong support for the monarchy, but because the proposal was a poorly thought out, overcomplicated mess which lacked detail and scared off voters.