You have to understand the background of this law, it may very well possible but time consuming and based on current defamation laws that were written for print media. In a recent high court case it was ruled that an online content posted on a Facebook business page of a media company the publisher is the business and in Australia the publisher is liable for defamation, not Facebook. So it is easier to sue the business (including small businesses) than the actual poster. This law will override this judgement and make explicit that the online poster is the one liable for defamation. In that case you can apply for a court order to unmask the person behind the account. If the social media companies fails to do so then THEY will be liable for the defamation.
Australian government will also fund test cases as for a ordinary person to mount a federal court case against the likes of Facebook is very expensive