It won't just hit Google and Facebook, but anybody who runs a social platform. Reddit, Hacker News, Twitter even Mastodon are all in the firing line. The Australian government has unilateral control over which sites are required to funnel money Murdoch trash instead of real (maybe even independent) journalism.
My prediction is people will move to social platforms that do let you share these links, and one by one they'll find themselves regulated out of existence when they get large enough to catch the attention of the government. Even worse - think about the ways this could be abused e.g. to shut down small outlets who committed the crime of linking to mainstream sources.
I believe this is far more despicable than anything Big Tech is doing, and global adoption would be the end of a free and open web.
You thought software patents constricted the flow of information? This is 10x worse.
Edit: Please, Aussies, call your MP and tell them your thoughts. Put aside any negative feelings about Big Tech for now, and think about the future of the web. This will eventually affect all of us who operate comment sections, blogs, forums and Mastodon instances.